# HG changeset patch
# User msirringhaus@suse.de
# Date 1559294891 -7200
#      Fri May 31 11:28:11 2019 +0200
# Node ID c2aa7198fb925e7fde96abf65b6f68b9b755f112
# Parent  8d1110b6918acc4e7d3f655d1e55f4b4ff630abe
Description: Add KDE integration to Firefox (toolkit parts)
Author: Wolfgang Rosenauer <wolfgang@rosenauer.org>
Author: Lubos Lunak <lunak@suse.com>
Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=140751
     https://bugzilla.novell.com/show_bug.cgi?id=170055

diff --git a/modules/libpref/Preferences.cpp b/modules/libpref/Preferences.cpp
--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -84,16 +84,17 @@
 #include "plbase64.h"
 #include "PLDHashTable.h"
 #include "plstr.h"
 #include "prlink.h"
 #include "xpcpublic.h"
 #ifdef MOZ_BACKGROUNDTASKS
 #  include "mozilla/BackgroundTasks.h"
 #endif
+#include "nsKDEUtils.h"
 
 #ifdef DEBUG
 #  include <map>
 #endif
 
 #ifdef MOZ_MEMORY
 #  include "mozmemory.h"
 #endif
@@ -4634,16 +4635,27 @@ nsresult Preferences::InitInitialObjects
     "unix.js"
 #  if defined(_AIX)
     ,
     "aix.js"
 #  endif
 #endif
   };
 
+  if(nsKDEUtils::kdeSession()) { // TODO what if some setup actually requires the helper?
+    for(int i = 0;
+        i < MOZ_ARRAY_LENGTH(specialFiles);
+        ++i ) {
+      if( *specialFiles[ i ] == '\0' ) {
+        specialFiles[ i ] = "kde.js";
+        break;
+      }
+    }
+  }
+
   rv = pref_LoadPrefsInDir(defaultPrefDir, specialFiles,
                            ArrayLength(specialFiles));
   if (NS_FAILED(rv)) {
     NS_WARNING("Error parsing application default preferences.");
   }
 
   // Load jar:$app/omni.jar!/defaults/preferences/*.js
   // or jar:$gre/omni.jar!/defaults/preferences/*.js.
@@ -4708,17 +4720,17 @@ nsresult Preferences::InitInitialObjects
       }
 
       nsCOMPtr<nsIFile> path = do_QueryInterface(elem);
       if (!path) {
         continue;
       }
 
       // Do we care if a file provided by this process fails to load?
-      pref_LoadPrefsInDir(path, nullptr, 0);
+      pref_LoadPrefsInDir(path, specialFiles, ArrayLength(specialFiles));
     }
   }
 
   if (XRE_IsParentProcess()) {
     SetupTelemetryPref();
   }
 
   if (aIsStartup) {
diff --git a/modules/libpref/moz.build b/modules/libpref/moz.build
--- a/modules/libpref/moz.build
+++ b/modules/libpref/moz.build
@@ -118,16 +118,20 @@ EXPORTS.mozilla += [
 ]
 EXPORTS.mozilla += sorted(["!" + g for g in gen_h])
 
 UNIFIED_SOURCES += [
     "Preferences.cpp",
     "SharedPrefMap.cpp",
 ]
 
+LOCAL_INCLUDES += [
+    '/toolkit/xre'
+]
+
 gen_all_tuple = tuple(gen_h + gen_cpp + gen_rs)
 
 GeneratedFile(
     *gen_all_tuple,
     script="init/generate_static_pref_list.py",
     entry_point="emit_code",
     inputs=["init/StaticPrefList.yaml"]
 )
diff --git a/python/mozbuild/mozpack/chrome/flags.py b/python/mozbuild/mozpack/chrome/flags.py
--- a/python/mozbuild/mozpack/chrome/flags.py
+++ b/python/mozbuild/mozpack/chrome/flags.py
@@ -229,16 +229,17 @@ class Flags(OrderedDict):
         "os": StringFlag,
         "osversion": VersionFlag,
         "abi": StringFlag,
         "platform": Flag,
         "xpcnativewrappers": Flag,
         "tablet": Flag,
         "process": StringFlag,
         "backgroundtask": StringFlag,
+        "desktop": StringFlag,
     }
     RE = re.compile(r"([!<>=]+)")
 
     def __init__(self, *flags):
         """
         Initialize a set of flags given in string form.
            flags = Flags('contentaccessible=yes', 'appversion>=3.5')
         """
diff --git a/python/mozbuild/mozpack/chrome/manifest.py b/python/mozbuild/mozpack/chrome/manifest.py
--- a/python/mozbuild/mozpack/chrome/manifest.py
+++ b/python/mozbuild/mozpack/chrome/manifest.py
@@ -39,16 +39,17 @@ class ManifestEntry(object):
         "os",
         "osversion",
         "abi",
         "xpcnativewrappers",
         "tablet",
         "process",
         "contentaccessible",
         "backgroundtask",
+        "desktop",
     ]
 
     def __init__(self, base, *flags):
         """
         Initialize a manifest entry with the given base path and flags.
         """
         self.base = base
         self.flags = Flags(*flags)
diff --git a/toolkit/components/downloads/moz.build b/toolkit/components/downloads/moz.build
--- a/toolkit/components/downloads/moz.build
+++ b/toolkit/components/downloads/moz.build
@@ -46,10 +46,14 @@ XPCOM_MANIFESTS += [
 
 if CONFIG["MOZ_PLACES"]:
     EXTRA_JS_MODULES += [
         "DownloadHistory.jsm",
     ]
 
 FINAL_LIBRARY = "xul"
 
+LOCAL_INCLUDES += [
+    '/toolkit/xre'
+]
+
 with Files("**"):
     BUG_COMPONENT = ("Toolkit", "Downloads API")
diff --git a/toolkit/mozapps/downloads/HelperAppDlg.jsm b/toolkit/mozapps/downloads/HelperAppDlg.jsm
--- a/toolkit/mozapps/downloads/HelperAppDlg.jsm
+++ b/toolkit/mozapps/downloads/HelperAppDlg.jsm
@@ -1252,36 +1252,66 @@ nsUnknownContentTypeDialog.prototype = {
         params.handlerApp &&
         params.handlerApp.executable &&
         params.handlerApp.executable.isFile()
       ) {
         // Remember the file they chose to run.
         this.chosenApp = params.handlerApp;
       }
     } else if ("@mozilla.org/applicationchooser;1" in Cc) {
-      var nsIApplicationChooser = Ci.nsIApplicationChooser;
-      var appChooser = Cc["@mozilla.org/applicationchooser;1"].createInstance(
-        nsIApplicationChooser
-      );
-      appChooser.init(
-        this.mDialog,
-        this.dialogElement("strings").getString("chooseAppFilePickerTitle")
-      );
-      var contentTypeDialogObj = this;
-      let appChooserCallback = function appChooserCallback_done(aResult) {
-        if (aResult) {
-          contentTypeDialogObj.chosenApp = aResult.QueryInterface(
-            Ci.nsILocalHandlerApp
-          );
-        }
-        contentTypeDialogObj.finishChooseApp();
-      };
-      appChooser.open(this.mLauncher.MIMEInfo.MIMEType, appChooserCallback);
-      // The finishChooseApp is called from appChooserCallback
-      return;
+      // handle the KDE case which is implemented in the filepicker
+      // therefore falling back to Gtk2 like behaviour if KDE is running
+      // FIXME this should be better handled in the nsIApplicationChooser
+      // interface
+      var env = Components.classes["@mozilla.org/process/environment;1"]
+                          .getService(Components.interfaces.nsIEnvironment);
+      if (env.get('KDE_FULL_SESSION') == "true")
+      {
+        var nsIFilePicker = Ci.nsIFilePicker;
+        var fp = Cc["@mozilla.org/filepicker;1"]
+                    .createInstance(nsIFilePicker);
+        fp.init(this.mDialog,
+                this.dialogElement("strings").getString("chooseAppFilePickerTitle"),
+                nsIFilePicker.modeOpen);
+
+        fp.appendFilters(nsIFilePicker.filterApps);
+
+        fp.open(aResult => {
+          if (aResult == nsIFilePicker.returnOK && fp.file) {
+            // Remember the file they chose to run.
+            var localHandlerApp =
+              Cc["@mozilla.org/uriloader/local-handler-app;1"].
+                         createInstance(Ci.nsILocalHandlerApp);
+            localHandlerApp.executable = fp.file;
+            this.chosenApp = localHandlerApp;
+          }
+          this.finishChooseApp();
+        });
+      } else {
+        var nsIApplicationChooser = Ci.nsIApplicationChooser;
+        var appChooser = Cc["@mozilla.org/applicationchooser;1"].createInstance(
+          nsIApplicationChooser
+        );
+        appChooser.init(
+          this.mDialog,
+          this.dialogElement("strings").getString("chooseAppFilePickerTitle")
+        );
+        var contentTypeDialogObj = this;
+        let appChooserCallback = function appChooserCallback_done(aResult) {
+          if (aResult) {
+            contentTypeDialogObj.chosenApp = aResult.QueryInterface(
+              Ci.nsILocalHandlerApp
+            );
+          }
+          contentTypeDialogObj.finishChooseApp();
+        };
+        appChooser.open(this.mLauncher.MIMEInfo.MIMEType, appChooserCallback);
+        // The finishChooseApp is called from appChooserCallback
+        return;
+      }
     } else {
       var nsIFilePicker = Ci.nsIFilePicker;
       var fp = Cc["@mozilla.org/filepicker;1"].createInstance(nsIFilePicker);
       fp.init(
         this.mDialog,
         this.dialogElement("strings").getString("chooseAppFilePickerTitle"),
         nsIFilePicker.modeOpen
       );
diff --git a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
--- a/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
+++ b/toolkit/system/unixproxy/nsUnixSystemProxySettings.cpp
@@ -13,16 +13,17 @@
 #include "nsPrintfCString.h"
 #include "nsNetCID.h"
 #include "nsNetUtil.h"
 #include "nsISupportsPrimitives.h"
 #include "nsIGSettingsService.h"
 #include "nsInterfaceHashtable.h"
 #include "mozilla/Attributes.h"
 #include "nsIURI.h"
+#include "nsKDEUtils.h"
 
 using namespace mozilla;
 
 class nsUnixSystemProxySettings final : public nsISystemProxySettings {
  public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSISYSTEMPROXYSETTINGS
 
@@ -36,16 +37,18 @@ class nsUnixSystemProxySettings final : 
   nsCOMPtr<nsIGSettingsCollection> mProxySettings;
   nsInterfaceHashtable<nsCStringHashKey, nsIGSettingsCollection>
       mSchemeProxySettings;
   nsresult GetProxyFromGSettings(const nsACString& aScheme,
                                  const nsACString& aHost, int32_t aPort,
                                  nsACString& aResult);
   nsresult SetProxyResultFromGSettings(const char* aKeyBase, const char* aType,
                                        nsACString& aResult);
+  nsresult GetProxyFromKDE(const nsACString& aScheme, const nsACString& aHost,
+                           PRInt32 aPort, nsACString& aResult);
 };
 
 NS_IMPL_ISUPPORTS(nsUnixSystemProxySettings, nsISystemProxySettings)
 
 NS_IMETHODIMP
 nsUnixSystemProxySettings::GetMainThreadOnly(bool* aMainThreadOnly) {
   // dbus prevents us from being threadsafe, but this routine should not block
   // anyhow
@@ -381,21 +384,50 @@ nsresult nsUnixSystemProxySettings::GetP
   return NS_OK;
 }
 
 nsresult nsUnixSystemProxySettings::GetProxyForURI(const nsACString& aSpec,
                                                    const nsACString& aScheme,
                                                    const nsACString& aHost,
                                                    const int32_t aPort,
                                                    nsACString& aResult) {
+  if (nsKDEUtils::kdeSupport())
+    return GetProxyFromKDE(aScheme, aHost, aPort, aResult);
+
   if (mProxySettings) {
     nsresult rv = GetProxyFromGSettings(aScheme, aHost, aPort, aResult);
     if (NS_SUCCEEDED(rv)) return rv;
   }
 
   return GetProxyFromEnvironment(aScheme, aHost, aPort, aResult);
 }
 
+nsresult
+nsUnixSystemProxySettings::GetProxyFromKDE(const nsACString& aScheme,
+                                           const nsACString& aHost,
+                                           PRInt32 aPort,
+                                           nsACString& aResult)
+{
+  nsAutoCString url;
+  url = aScheme;
+  url += "://";
+  url += aHost;
+  if( aPort >= 0 )
+  {
+    url += ":";
+    url += nsPrintfCString("%d", aPort);
+  }
+  nsTArray<nsCString> command;
+  command.AppendElement( "GETPROXY"_ns );
+  command.AppendElement( url );
+  nsTArray<nsCString> result;
+  if( !nsKDEUtils::command( command, &result ) || result.Length() != 1 )
+    return NS_ERROR_FAILURE;
+  aResult = result[0];
+  return NS_OK;
+}
+
+
 NS_IMPL_COMPONENT_FACTORY(nsUnixSystemProxySettings) {
   auto result = MakeRefPtr<nsUnixSystemProxySettings>();
   result->Init();
   return result.forget().downcast<nsISupports>();
 }
diff --git a/toolkit/xre/moz.build b/toolkit/xre/moz.build
--- a/toolkit/xre/moz.build
+++ b/toolkit/xre/moz.build
@@ -92,17 +92,19 @@ elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "co
         "../components/printingui",
     ]
 elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "uikit":
     UNIFIED_SOURCES += [
         "nsNativeAppSupportDefault.cpp",
         "UIKitDirProvider.mm",
     ]
 elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
+    EXPORTS += ['nsKDEUtils.h']
     UNIFIED_SOURCES += [
+        "nsKDEUtils.cpp",
         "nsNativeAppSupportUnix.cpp",
     ]
     CXXFLAGS += CONFIG["MOZ_X11_SM_CFLAGS"]
 else:
     UNIFIED_SOURCES += [
         "nsNativeAppSupportDefault.cpp",
     ]
 
diff --git a/toolkit/xre/nsKDEUtils.cpp b/toolkit/xre/nsKDEUtils.cpp
new file mode 100644
--- /dev/null
+++ b/toolkit/xre/nsKDEUtils.cpp
@@ -0,0 +1,321 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsKDEUtils.h"
+#include "nsIWidget.h"
+#include "nsISupportsPrimitives.h"
+#include "nsIMutableArray.h"
+#include "nsComponentManagerUtils.h"
+#include "nsArrayUtils.h"
+
+#include <gtk/gtk.h>
+
+#include <limits.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <sys/resource.h>
+#include <unistd.h>
+#include <X11/Xlib.h>
+// copied from X11/X.h as a hack since for an unknown
+// reason it's not picked up from X11/X.h
+#ifndef None
+#define None                 0L /* universal null resource or null atom */
+#endif
+
+//#define DEBUG_KDE
+#ifdef DEBUG_KDE
+#define KMOZILLAHELPER "kmozillahelper"
+#else
+// not need for lib64, it's a binary
+#define KMOZILLAHELPER "/usr/lib/mozilla/kmozillahelper"
+#endif
+
+#define KMOZILLAHELPER_VERSION 6
+#define MAKE_STR2( n ) #n
+#define MAKE_STR( n ) MAKE_STR2( n )
+
+static bool getKdeSession()
+{
+    if (PR_GetEnv("KDE_FULL_SESSION"))
+    {
+      return true;
+    }
+    return false;
+}
+
+static bool getKdeSupport()
+    {
+    nsTArray<nsCString> command;
+    command.AppendElement( "CHECK"_ns );
+    command.AppendElement( "KMOZILLAHELPER_VERSION"_ns );
+    bool kde = nsKDEUtils::command( command );
+#ifdef DEBUG_KDE
+    fprintf( stderr, "KDE RUNNING %d\n", kde );
+#endif
+    return kde;
+    }
+
+nsKDEUtils::nsKDEUtils()
+    : commandFile( NULL )
+    , replyFile( NULL )
+    {
+    }
+
+nsKDEUtils::~nsKDEUtils()
+    {
+//    closeHelper(); not actually useful, exiting will close the fd too
+    }
+
+nsKDEUtils* nsKDEUtils::self()
+    {
+    static nsKDEUtils s;
+    return &s;
+    }
+
+static bool helperRunning = false;
+static bool helperFailed = false;
+
+bool nsKDEUtils::kdeSession()
+    {
+    static bool session = getKdeSession();
+    return session;
+    }
+
+bool nsKDEUtils::kdeSupport()
+    {
+    static bool support = kdeSession() && getKdeSupport();
+    return support && helperRunning;
+    }
+
+struct nsKDECommandData
+    {
+    FILE* file;
+    nsTArray<nsCString>* output;
+    GMainLoop* loop;
+    bool success;
+    };
+
+static gboolean kdeReadFunc( GIOChannel*, GIOCondition, gpointer data )
+    {
+    nsKDECommandData* p = static_cast< nsKDECommandData* >( data );
+    char buf[ 8192 ]; // TODO big enough
+    bool command_done = false;
+    bool command_failed = false;
+    while( !command_done && !command_failed && fgets( buf, 8192, p->file ) != NULL )
+        { // TODO what if the kernel splits a line into two chunks?
+//#ifdef DEBUG_KDE
+//        fprintf( stderr, "READ: %s %d\n", buf, feof( p->file ));
+//#endif
+        if( char* eol = strchr( buf, '\n' ))
+            *eol = '\0';
+        command_done = ( strcmp( buf, "\\1" ) == 0 );
+        command_failed = ( strcmp( buf, "\\0" ) == 0 );
+        nsAutoCString line( buf );
+        line.ReplaceSubstring( "\\n", "\n" );
+        line.ReplaceSubstring( "\\" "\\", "\\" ); //  \\ -> \ , i.e. unescape
+        if( p->output && !( command_done || command_failed ))
+            p->output->AppendElement( nsCString( buf )); // TODO utf8?
+        }
+    bool quit = false;
+    if( feof( p->file ) || command_failed )
+        {
+        quit = true;
+        p->success = false;
+        }
+    if( command_done )
+        { // reading one reply finished
+        quit = true;
+        p->success = true;
+        }
+    if( quit )
+        {
+        if( p->loop )
+            g_main_loop_quit( p->loop );
+        return FALSE;
+        }
+    return TRUE;
+    }
+
+bool nsKDEUtils::command( const nsTArray<nsCString>& command, nsTArray<nsCString>* output )
+    {
+    return self()->internalCommand( command, NULL, false, output );
+    }
+
+bool nsKDEUtils::command( nsIArray* command, nsIArray** output)
+    {
+    nsTArray<nsCString> in;
+    PRUint32 length;
+    command->GetLength( &length );
+    for ( PRUint32 i = 0; i < length; i++ )
+        {
+        nsCOMPtr<nsISupportsCString> str = do_QueryElementAt( command, i );
+        if( str )
+            {
+            nsAutoCString s;
+            str->GetData( s );
+            in.AppendElement( s );
+            }
+        }
+
+    nsTArray<nsCString> out;
+    bool ret = self()->internalCommand( in, NULL, false, &out );
+
+    if ( !output ) return ret;
+
+    nsCOMPtr<nsIMutableArray> result = do_CreateInstance( NS_ARRAY_CONTRACTID );
+    if ( !result ) return false;
+
+    for ( PRUint32 i = 0; i < out.Length(); i++ )
+        {
+        nsCOMPtr<nsISupportsCString> rstr = do_CreateInstance( NS_SUPPORTS_CSTRING_CONTRACTID );
+        if ( !rstr ) return false;
+
+        rstr->SetData( out[i] );
+        result->AppendElement( rstr );
+        }
+
+    NS_ADDREF( *output = result);
+    return ret;
+    }
+
+
+bool nsKDEUtils::commandBlockUi( const nsTArray<nsCString>& command, GtkWindow* parent, nsTArray<nsCString>* output )
+    {
+    return self()->internalCommand( command, parent, true, output );
+    }
+
+bool nsKDEUtils::internalCommand( const nsTArray<nsCString>& command, GtkWindow* parent, bool blockUi,
+    nsTArray<nsCString>* output )
+    {
+    if( !startHelper())
+        return false;
+    feedCommand( command );
+    // do not store the data in 'this' but in extra structure, just in case there
+    // is reentrancy (can there be? the event loop is re-entered)
+    nsKDECommandData data;
+    data.file = replyFile;
+    data.output = output;
+    data.success = false;
+    if( blockUi )
+        {
+        data.loop = g_main_loop_new( NULL, FALSE );
+        GtkWidget* window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
+        if( parent && gtk_window_get_group(parent) )
+            gtk_window_group_add_window( gtk_window_get_group(parent), GTK_WINDOW( window ));
+        gtk_widget_realize( window );
+        gtk_widget_set_sensitive( window, TRUE );
+        gtk_grab_add( window );
+        GIOChannel* channel = g_io_channel_unix_new( fileno( data.file ));
+        g_io_add_watch( channel, static_cast< GIOCondition >( G_IO_IN | G_IO_ERR | G_IO_HUP ), kdeReadFunc, &data );
+        g_io_channel_unref( channel );
+        g_main_loop_run( data.loop );
+        g_main_loop_unref( data.loop );
+        gtk_grab_remove( window );
+        gtk_widget_destroy( window );
+        }
+    else
+        {
+        data.loop = NULL;
+        while( kdeReadFunc( NULL, static_cast< GIOCondition >( 0 ), &data ))
+            ;
+        }
+    return data.success;
+    }
+
+bool nsKDEUtils::startHelper()
+    {
+    if( helperRunning )
+        return true;
+    if( helperFailed )
+        return false;
+    helperFailed = true;
+    int fdcommand[ 2 ];
+    int fdreply[ 2 ];
+    if( pipe( fdcommand ) < 0 )
+        return false;
+    if( pipe( fdreply ) < 0 )
+        {
+        close( fdcommand[ 0 ] );
+        close( fdcommand[ 1 ] );
+        return false;
+        }
+    char* args[ 2 ] = { const_cast< char* >( KMOZILLAHELPER ), NULL };
+    switch( fork())
+        {
+        case -1:
+            {
+            close( fdcommand[ 0 ] );
+            close( fdcommand[ 1 ] );
+            close( fdreply[ 0 ] );
+            close( fdreply[ 1 ] );
+            return false;
+            }
+        case 0: // child
+            {
+            if( dup2( fdcommand[ 0 ], STDIN_FILENO ) < 0 )
+                _exit( 1 );
+            if( dup2( fdreply[ 1 ], STDOUT_FILENO ) < 0 )
+                _exit( 1 );
+            int maxfd = 1024; // close all other fds
+            struct rlimit rl;
+            if( getrlimit( RLIMIT_NOFILE, &rl ) == 0 )
+                maxfd = rl.rlim_max;
+            for( int i = 3;
+                 i < maxfd;
+                 ++i )
+                close( i );
+#ifdef DEBUG_KDE
+            execvp( KMOZILLAHELPER, args );
+#else
+            execv( KMOZILLAHELPER, args );
+#endif
+            _exit( 1 ); // failed
+            }
+        default: // parent
+            {
+            commandFile = fdopen( fdcommand[ 1 ], "w" );
+            replyFile = fdopen( fdreply[ 0 ], "r" );
+            close( fdcommand[ 0 ] );
+            close( fdreply[ 1 ] );
+            if( commandFile == NULL || replyFile == NULL )
+                {
+                closeHelper();
+                return false;
+                }
+            // ok, helper ready, getKdeRunning() will check if it works
+            }
+        }
+    helperFailed = false;
+    helperRunning = true;
+    return true;
+    }
+
+void nsKDEUtils::closeHelper()
+    {
+    if( commandFile != NULL )
+        fclose( commandFile ); // this will also make the helper quit
+    if( replyFile != NULL )
+        fclose( replyFile );
+    helperRunning = false;
+    }
+
+void nsKDEUtils::feedCommand( const nsTArray<nsCString>& command )
+    {
+    for( int i = 0;
+         i < command.Length();
+         ++i )
+        {
+        nsCString line = command[ i ];
+        line.ReplaceSubstring( "\\", "\\" "\\" ); // \ -> \\ , i.e. escape
+        line.ReplaceSubstring( "\n", "\\n" );
+#ifdef DEBUG_KDE
+        fprintf( stderr, "COMM: %s\n", line.get());
+#endif
+        fputs( line.get(), commandFile );
+        fputs( "\n", commandFile );
+        }
+    fputs( "\\E\n", commandFile ); // done as \E, so it cannot happen in normal data
+    fflush( commandFile );
+    }
diff --git a/toolkit/xre/nsKDEUtils.h b/toolkit/xre/nsKDEUtils.h
new file mode 100644
--- /dev/null
+++ b/toolkit/xre/nsKDEUtils.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsKDEUtils_h__
+#define nsKDEUtils_h__
+
+#include "nsString.h"
+#include "nsTArray.h"
+#include <stdio.h>
+
+typedef struct _GtkWindow GtkWindow;
+
+class nsIArray;
+
+class NS_EXPORT nsKDEUtils
+    {
+    public:
+        /* Returns true if running inside a KDE session (regardless of whether there is KDE
+           support available for Firefox). This should be used e.g. when determining
+           dialog button order but not for code that requires the KDE support. */
+        static bool kdeSession();
+        /* Returns true if running inside a KDE session and KDE support is available
+           for Firefox. This should be used everywhere where the external helper is needed. */
+        static bool kdeSupport();
+        /* Executes the given helper command, returns true if helper returned success. */
+        static bool command( const nsTArray<nsCString>& command, nsTArray<nsCString>* output = NULL );
+        static bool command( nsIArray* command, nsIArray** output = NULL );
+        /* Like command(), but additionally blocks the parent widget like if there was
+           a modal dialog shown and enters the event loop (i.e. there are still paint updates,
+           this is for commands that take long). */
+        static bool commandBlockUi( const nsTArray<nsCString>& command, GtkWindow* parent, nsTArray<nsCString>* output = NULL );
+
+    private:
+        nsKDEUtils();
+        ~nsKDEUtils();
+        static nsKDEUtils* self();
+        bool startHelper();
+        void closeHelper();
+        void feedCommand( const nsTArray<nsCString>& command );
+        bool internalCommand( const nsTArray<nsCString>& command, GtkWindow* parent, bool isParent,
+            nsTArray<nsCString>* output );
+        FILE* commandFile;
+        FILE* replyFile;
+    };
+
+#endif // nsKDEUtils
diff --git a/uriloader/exthandler/HandlerServiceParent.cpp b/uriloader/exthandler/HandlerServiceParent.cpp
--- a/uriloader/exthandler/HandlerServiceParent.cpp
+++ b/uriloader/exthandler/HandlerServiceParent.cpp
@@ -7,17 +7,17 @@
 #include "mozilla/ipc/ProtocolUtils.h"
 #include "mozilla/Logging.h"
 #include "HandlerServiceParent.h"
 #include "nsIHandlerService.h"
 #include "nsIMIMEInfo.h"
 #include "ContentHandlerService.h"
 #include "nsStringEnumerator.h"
 #ifdef MOZ_WIDGET_GTK
-#  include "unix/nsGNOMERegistry.h"
+#  include "unix/nsCommonRegistry.h"
 #endif
 
 using mozilla::dom::ContentHandlerService;
 using mozilla::dom::HandlerApp;
 using mozilla::dom::HandlerInfo;
 using mozilla::dom::RemoteHandlerApp;
 
 namespace {
@@ -299,17 +299,17 @@ mozilla::ipc::IPCResult HandlerServicePa
 mozilla::ipc::IPCResult HandlerServiceParent::RecvExistsForProtocolOS(
     const nsCString& aProtocolScheme, bool* aHandlerExists) {
   if (aProtocolScheme.Length() > MAX_SCHEME_LENGTH) {
     *aHandlerExists = false;
     return IPC_OK();
   }
 #ifdef MOZ_WIDGET_GTK
   // Check the GNOME registry for a protocol handler
-  *aHandlerExists = nsGNOMERegistry::HandlerExists(aProtocolScheme.get());
+  *aHandlerExists = nsCommonRegistry::HandlerExists(aProtocolScheme.get());
 #else
   *aHandlerExists = false;
 #endif
   return IPC_OK();
 }
 
 /*
  * Check if a handler exists for the provided protocol. Check the datastore
@@ -328,17 +328,17 @@ mozilla::ipc::IPCResult HandlerServicePa
   nsCOMPtr<nsIExternalProtocolService> protoSvc =
       do_GetService(NS_EXTERNALPROTOCOLSERVICE_CONTRACTID, &rv);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     *aHandlerExists = false;
     return IPC_OK();
   }
   rv = protoSvc->ExternalProtocolHandlerExists(aProtocolScheme.get(),
                                                aHandlerExists);
-
+##
   if (NS_WARN_IF(NS_FAILED(rv))) {
     *aHandlerExists = false;
   }
 #else
   MOZ_RELEASE_ASSERT(false, "No implementation on this platform.");
   *aHandlerExists = false;
 #endif
   return IPC_OK();
diff --git a/uriloader/exthandler/moz.build b/uriloader/exthandler/moz.build
--- a/uriloader/exthandler/moz.build
+++ b/uriloader/exthandler/moz.build
@@ -78,17 +78,19 @@ elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "ui
 else:
     # These files can't be built in unified mode because they redefine LOG.
     SOURCES += [
         osdir + "/nsOSHelperAppService.cpp",
     ]
 
 if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
     UNIFIED_SOURCES += [
+        "unix/nsCommonRegistry.cpp",
         "unix/nsGNOMERegistry.cpp",
+        "unix/nsKDERegistry.cpp",
         "unix/nsMIMEInfoUnix.cpp",
     ]
 elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "android":
     UNIFIED_SOURCES += [
         "android/nsMIMEInfoAndroid.cpp",
     ]
 elif CONFIG["MOZ_WIDGET_TOOLKIT"] == "windows":
     UNIFIED_SOURCES += [
@@ -126,16 +128,17 @@ include("/ipc/chromium/chromium-config.m
 FINAL_LIBRARY = "xul"
 
 LOCAL_INCLUDES += [
     "/docshell/base",
     "/dom/base",
     "/dom/ipc",
     "/netwerk/base",
     "/netwerk/protocol/http",
+    "/toolkit/xre",
 ]
 
 if CONFIG["MOZ_ENABLE_DBUS"]:
     CXXFLAGS += CONFIG["MOZ_DBUS_CFLAGS"]
 
 if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
     CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
     CXXFLAGS += CONFIG["MOZ_DBUS_GLIB_CFLAGS"]
diff --git a/uriloader/exthandler/unix/nsCommonRegistry.cpp b/uriloader/exthandler/unix/nsCommonRegistry.cpp
new file mode 100644
--- /dev/null
+++ b/uriloader/exthandler/unix/nsCommonRegistry.cpp
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsCommonRegistry.h"
+
+#include "nsGNOMERegistry.h"
+#include "nsKDERegistry.h"
+#include "nsString.h"
+#include "nsKDEUtils.h"
+
+/* static */ bool
+nsCommonRegistry::HandlerExists(const char *aProtocolScheme)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::HandlerExists( aProtocolScheme );
+    return nsGNOMERegistry::HandlerExists( aProtocolScheme );
+}
+
+/* static */ nsresult
+nsCommonRegistry::LoadURL(nsIURI *aURL)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::LoadURL( aURL );
+    return nsGNOMERegistry::LoadURL( aURL );
+}
+
+/* static */ void
+nsCommonRegistry::GetAppDescForScheme(const nsACString& aScheme,
+                                     nsAString& aDesc)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetAppDescForScheme( aScheme, aDesc );
+    return nsGNOMERegistry::GetAppDescForScheme( aScheme, aDesc );
+}
+
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsCommonRegistry::GetFromExtension(const nsACString& aFileExt)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetFromExtension( aFileExt );
+    return nsGNOMERegistry::GetFromExtension( aFileExt );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsCommonRegistry::GetFromType(const nsACString& aMIMEType)
+{
+    if( nsKDEUtils::kdeSupport())
+        return nsKDERegistry::GetFromType( aMIMEType );
+    return nsGNOMERegistry::GetFromType( aMIMEType );
+}
diff --git a/uriloader/exthandler/unix/nsCommonRegistry.h b/uriloader/exthandler/unix/nsCommonRegistry.h
new file mode 100644
--- /dev/null
+++ b/uriloader/exthandler/unix/nsCommonRegistry.h
@@ -0,0 +1,28 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsCommonRegistry_h__
+#define nsCommonRegistry_h__
+
+#include "nsIURI.h"
+#include "nsCOMPtr.h"
+
+class nsMIMEInfoBase;
+
+class nsCommonRegistry
+{
+ public:
+  static bool HandlerExists(const char *aProtocolScheme);
+
+  static nsresult LoadURL(nsIURI *aURL);
+
+  static void GetAppDescForScheme(const nsACString& aScheme,
+                                  nsAString& aDesc);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromExtension(const nsACString& aFileExt);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromType(const nsACString& aMIMEType);
+};
+
+#endif
diff --git a/uriloader/exthandler/unix/nsKDERegistry.cpp b/uriloader/exthandler/unix/nsKDERegistry.cpp
new file mode 100644
--- /dev/null
+++ b/uriloader/exthandler/unix/nsKDERegistry.cpp
@@ -0,0 +1,89 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/StaticPrefs_browser.h"
+#include "nsKDERegistry.h"
+#include "prlink.h"
+#include "prmem.h"
+#include "nsString.h"
+#include "nsMIMEInfoUnix.h"
+#include "nsKDEUtils.h"
+
+/* static */ bool
+nsKDERegistry::HandlerExists(const char *aProtocolScheme)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( "HANDLEREXISTS"_ns );
+    command.AppendElement( nsAutoCString( aProtocolScheme ));
+    return nsKDEUtils::command( command );
+}
+
+/* static */ nsresult
+nsKDERegistry::LoadURL(nsIURI *aURL)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( "OPEN"_ns );
+    nsCString url;
+    aURL->GetSpec( url );
+    command.AppendElement( url );
+    bool rv = nsKDEUtils::command( command );
+    if (!rv)
+      return NS_ERROR_FAILURE;
+
+    return NS_OK;
+}
+
+/* static */ void
+nsKDERegistry::GetAppDescForScheme(const nsACString& aScheme,
+                                     nsAString& aDesc)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( "GETAPPDESCFORSCHEME"_ns );
+    command.AppendElement( aScheme );
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::command( command, &output ) && output.Length() == 1 )
+        CopyUTF8toUTF16( output[ 0 ], aDesc );
+}
+
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromExtension(const nsACString& aFileExt)
+{
+    NS_ASSERTION(aFileExt[0] != '.', "aFileExt shouldn't start with a dot");
+    nsTArray<nsCString> command;
+    command.AppendElement( "GETFROMEXTENSION"_ns );
+    command.AppendElement( aFileExt );
+    return GetFromHelper( command );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromType(const nsACString& aMIMEType)
+{
+    nsTArray<nsCString> command;
+    command.AppendElement( "GETFROMTYPE"_ns );
+    command.AppendElement( aMIMEType );
+    return GetFromHelper( command );
+}
+
+/* static */ already_AddRefed<nsMIMEInfoBase>
+nsKDERegistry::GetFromHelper(const nsTArray<nsCString>& command)
+{
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::command( command, &output ) && output.Length() == 3 )
+        {
+        nsCString mimetype = output[ 0 ];
+        RefPtr<nsMIMEInfoUnix> mimeInfo = new nsMIMEInfoUnix( mimetype );
+        NS_ENSURE_TRUE(mimeInfo, nullptr);
+        nsCString description = output[ 1 ];
+        mimeInfo->SetDescription(NS_ConvertUTF8toUTF16(description));
+        nsCString handlerAppName = output[ 2 ];
+        mozilla::StaticPrefs::browser_download_improvements_to_download_panel()
+            ? mimeInfo->SetPreferredAction(nsIMIMEInfo::saveToDisk)
+            : mimeInfo->SetPreferredAction(nsIMIMEInfo::useSystemDefault);
+        mimeInfo->SetDefaultDescription(NS_ConvertUTF8toUTF16(handlerAppName));
+        return mimeInfo.forget();
+        }
+    return nullptr;
+}
diff --git a/uriloader/exthandler/unix/nsKDERegistry.h b/uriloader/exthandler/unix/nsKDERegistry.h
new file mode 100644
--- /dev/null
+++ b/uriloader/exthandler/unix/nsKDERegistry.h
@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsKDERegistry_h__
+#define nsKDERegistry_h__
+
+#include "nsIURI.h"
+#include "nsCOMPtr.h"
+#include "nsTArray.h"
+
+class nsMIMEInfoBase;
+//class nsAutoCString;
+//class nsCString;
+
+class nsKDERegistry
+{
+ public:
+  static bool HandlerExists(const char *aProtocolScheme);
+
+  static nsresult LoadURL(nsIURI *aURL);
+
+  static void GetAppDescForScheme(const nsACString& aScheme,
+                                  nsAString& aDesc);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromExtension(const nsACString& aFileExt);
+
+  static already_AddRefed<nsMIMEInfoBase> GetFromType(const nsACString& aMIMEType);
+ private:
+  static already_AddRefed<nsMIMEInfoBase> GetFromHelper(const nsTArray<nsCString>& command);
+
+};
+
+#endif //nsKDERegistry_h__
diff --git a/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp b/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
--- a/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
+++ b/uriloader/exthandler/unix/nsMIMEInfoUnix.cpp
@@ -1,46 +1,49 @@
 /* -*- Mode: C++; tab-width: 3; indent-tabs-mode: nil; c-basic-offset: 2 -*-
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsMIMEInfoUnix.h"
-#include "nsGNOMERegistry.h"
+#include "nsCommonRegistry.h"
 #include "nsIGIOService.h"
 #include "nsNetCID.h"
 #include "nsIIOService.h"
 #ifdef MOZ_ENABLE_DBUS
 #  include "nsDBusHandlerApp.h"
 #endif
+#if defined(XP_UNIX) && !defined(XP_MACOSX)
+#include "nsKDEUtils.h"
+#endif
 
 nsresult nsMIMEInfoUnix::LoadUriInternal(nsIURI* aURI) {
-  return nsGNOMERegistry::LoadURL(aURI);
+  return nsCommonRegistry::LoadURL(aURI);
 }
 
 NS_IMETHODIMP
 nsMIMEInfoUnix::GetHasDefaultHandler(bool* _retval) {
   // if mDefaultApplication is set, it means the application has been set from
   // either /etc/mailcap or ${HOME}/.mailcap, in which case we don't want to
   // give the GNOME answer.
   if (mDefaultApplication) return nsMIMEInfoImpl::GetHasDefaultHandler(_retval);
 
   *_retval = false;
 
   if (mClass == eProtocolInfo) {
-    *_retval = nsGNOMERegistry::HandlerExists(mSchemeOrType.get());
+    *_retval = nsCommonRegistry::HandlerExists(mSchemeOrType.get());
   } else {
     RefPtr<nsMIMEInfoBase> mimeInfo =
-        nsGNOMERegistry::GetFromType(mSchemeOrType);
+        nsCommonRegistry::GetFromType(mSchemeOrType);
     if (!mimeInfo) {
       nsAutoCString ext;
       nsresult rv = GetPrimaryExtension(ext);
       if (NS_SUCCEEDED(rv)) {
-        mimeInfo = nsGNOMERegistry::GetFromExtension(ext);
+        mimeInfo = nsCommonRegistry::GetFromExtension(ext);
       }
     }
     if (mimeInfo) *_retval = true;
   }
 
   if (*_retval) return NS_OK;
 
   return NS_OK;
@@ -50,16 +53,33 @@ nsresult nsMIMEInfoUnix::LaunchDefaultWi
   // if mDefaultApplication is set, it means the application has been set from
   // either /etc/mailcap or ${HOME}/.mailcap, in which case we don't want to
   // give the GNOME answer.
   if (mDefaultApplication) return nsMIMEInfoImpl::LaunchDefaultWithFile(aFile);
 
   nsAutoCString nativePath;
   aFile->GetNativePath(nativePath);
 
+  if( nsKDEUtils::kdeSupport()) {
+    bool supports;
+    if( NS_SUCCEEDED( GetHasDefaultHandler( &supports )) && supports ) {
+      nsTArray<nsCString> command;
+      command.AppendElement( "OPEN"_ns );
+      command.AppendElement( nativePath );
+      command.AppendElement( "MIMETYPE"_ns );
+      command.AppendElement( mSchemeOrType );
+      if( nsKDEUtils::command( command ))
+        return NS_OK;
+    }
+    if (!mDefaultApplication)
+      return NS_ERROR_FILE_NOT_FOUND;
+
+    return LaunchWithIProcess(mDefaultApplication, nativePath);
+  }
+
   nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (!giovfs) {
     return NS_ERROR_FAILURE;
   }
 
   // nsGIOMimeApp->Launch wants a URI string instead of local file
   nsresult rv;
   nsCOMPtr<nsIIOService> ioservice =
diff --git a/uriloader/exthandler/unix/nsOSHelperAppService.cpp b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
--- a/uriloader/exthandler/unix/nsOSHelperAppService.cpp
+++ b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
@@ -5,17 +5,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include <sys/types.h>
 #include <sys/stat.h>
 
 #include "nsOSHelperAppService.h"
 #include "nsMIMEInfoUnix.h"
 #ifdef MOZ_WIDGET_GTK
-#  include "nsGNOMERegistry.h"
+#  include "nsCommonRegistry.h"
 #  ifdef MOZ_BUILD_APP_IS_BROWSER
 #    include "nsIToolkitShellService.h"
 #    include "nsIGNOMEShellService.h"
 #  endif
 #endif
 #include "nsISupports.h"
 #include "nsString.h"
 #include "nsReadableUtils.h"
@@ -1025,17 +1025,17 @@ nsresult nsOSHelperAppService::GetHandle
 
 nsresult nsOSHelperAppService::OSProtocolHandlerExists(
     const char* aProtocolScheme, bool* aHandlerExists) {
   nsresult rv = NS_OK;
 
   if (!XRE_IsContentProcess()) {
 #ifdef MOZ_WIDGET_GTK
     // Check the GNOME registry for a protocol handler
-    *aHandlerExists = nsGNOMERegistry::HandlerExists(aProtocolScheme);
+    *aHandlerExists = nsCommonRegistry::HandlerExists(aProtocolScheme);
 #else
     *aHandlerExists = false;
 #endif
   } else {
     *aHandlerExists = false;
     nsCOMPtr<nsIHandlerService> handlerSvc =
         do_GetService(NS_HANDLERSERVICE_CONTRACTID, &rv);
     if (NS_SUCCEEDED(rv) && handlerSvc) {
@@ -1045,17 +1045,17 @@ nsresult nsOSHelperAppService::OSProtoco
   }
 
   return rv;
 }
 
 NS_IMETHODIMP nsOSHelperAppService::GetApplicationDescription(
     const nsACString& aScheme, nsAString& _retval) {
 #ifdef MOZ_WIDGET_GTK
-  nsGNOMERegistry::GetAppDescForScheme(aScheme, _retval);
+  nsCommonRegistry::GetAppDescForScheme(aScheme, _retval);
   return _retval.IsEmpty() ? NS_ERROR_NOT_AVAILABLE : NS_OK;
 #else
   return NS_ERROR_NOT_AVAILABLE;
 #endif
 }
 
 NS_IMETHODIMP nsOSHelperAppService::IsCurrentAppOSDefaultForProtocol(
     const nsACString& aScheme, bool* _retval) {
@@ -1148,17 +1148,17 @@ already_AddRefed<nsMIMEInfoBase> nsOSHel
   nsresult rv =
       LookUpTypeAndDescription(NS_ConvertUTF8toUTF16(aFileExt), majorType,
                                minorType, mime_types_description, true);
 
   if (NS_FAILED(rv) || majorType.IsEmpty()) {
 #ifdef MOZ_WIDGET_GTK
     LOG(("Looking in GNOME registry\n"));
     RefPtr<nsMIMEInfoBase> gnomeInfo =
-        nsGNOMERegistry::GetFromExtension(aFileExt);
+        nsCommonRegistry::GetFromExtension(aFileExt);
     if (gnomeInfo) {
       LOG(("Got MIMEInfo from GNOME registry\n"));
       return gnomeInfo.forget();
     }
 #endif
 
     rv = LookUpTypeAndDescription(NS_ConvertUTF8toUTF16(aFileExt), majorType,
                                   minorType, mime_types_description, false);
@@ -1261,17 +1261,17 @@ already_AddRefed<nsMIMEInfoBase> nsOSHel
 
   // Now look up our extensions
   nsAutoString extensions, mime_types_description;
   LookUpExtensionsAndDescription(majorType, minorType, extensions,
                                  mime_types_description);
 
 #ifdef MOZ_WIDGET_GTK
   if (handler.IsEmpty()) {
-    RefPtr<nsMIMEInfoBase> gnomeInfo = nsGNOMERegistry::GetFromType(aMIMEType);
+    RefPtr<nsMIMEInfoBase> gnomeInfo = nsCommonRegistry::GetFromType(aMIMEType);
     if (gnomeInfo) {
       LOG(
           ("Got MIMEInfo from GNOME registry without extensions; setting them "
            "to %s\n",
            NS_LossyConvertUTF16toASCII(extensions).get()));
 
       NS_ASSERTION(!gnomeInfo->HasExtensions(), "How'd that happen?");
       gnomeInfo->SetFileExtensions(NS_ConvertUTF16toUTF8(extensions));
diff --git a/widget/gtk/moz.build b/widget/gtk/moz.build
--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -136,16 +136,17 @@ FINAL_LIBRARY = "xul"
 
 LOCAL_INCLUDES += [
     "/layout/base",
     "/layout/forms",
     "/layout/generic",
     "/layout/xul",
     "/other-licenses/atk-1.0",
     "/third_party/cups/include",
+    "/toolkit/xre",
     "/widget",
     "/widget/headless",
 ]
 
 if CONFIG["MOZ_X11"]:
     LOCAL_INCLUDES += [
         "/widget/x11",
     ]
diff --git a/widget/gtk/nsFilePicker.cpp b/widget/gtk/nsFilePicker.cpp
--- a/widget/gtk/nsFilePicker.cpp
+++ b/widget/gtk/nsFilePicker.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include <dlfcn.h>
 #include <gtk/gtk.h>
+#include <gdk/gdkx.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include "mozilla/Types.h"
 #include "nsGtkUtils.h"
 #include "nsIFileURL.h"
 #include "nsIGIOService.h"
@@ -22,16 +23,18 @@
 #include "nsMemory.h"
 #include "nsEnumeratorUtils.h"
 #include "nsNetUtil.h"
 #include "nsReadableUtils.h"
 #include "MozContainer.h"
 #include "WidgetUtilsGtk.h"
 
 #include "nsFilePicker.h"
+#include "nsKDEUtils.h"
+#include "nsURLHelper.h"
 
 #undef LOG
 #ifdef MOZ_LOGGING
 #  include "mozilla/Logging.h"
 #  include "nsTArray.h"
 #  include "Units.h"
 extern mozilla::LazyLogModule gWidgetLog;
 #  define LOG(args) MOZ_LOG(gWidgetLog, mozilla::LogLevel::Debug, args)
@@ -236,17 +239,19 @@ nsFilePicker::AppendFilters(int32_t aFil
   mAllowURLs = !!(aFilterMask & filterAllowURLs);
   return nsBaseFilePicker::AppendFilters(aFilterMask);
 }
 
 NS_IMETHODIMP
 nsFilePicker::AppendFilter(const nsAString& aTitle, const nsAString& aFilter) {
   if (aFilter.EqualsLiteral("..apps")) {
     // No platform specific thing we can do here, really....
-    return NS_OK;
+    // Unless it's KDE.
+    if( mMode != modeOpen || !nsKDEUtils::kdeSupport())
+      return NS_OK;
   }
 
   nsAutoCString filter, name;
   CopyUTF16toUTF8(aFilter, filter);
   CopyUTF16toUTF8(aTitle, name);
 
   mFilters.AppendElement(filter);
   mFilterNames.AppendElement(name);
@@ -346,16 +351,39 @@ nsresult nsFilePicker::Show(int16_t* aRe
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsFilePicker::Open(nsIFilePickerShownCallback* aCallback) {
   // Can't show two dialogs concurrently with the same filepicker
   if (mRunning) return NS_ERROR_NOT_AVAILABLE;
 
+  // KDE file picker is not handled via callback
+  if( nsKDEUtils::kdeSupport()) {
+    mCallback = aCallback;
+    mRunning = true;
+    NS_ADDREF_THIS();
+    g_idle_add([](gpointer data) -> gboolean {
+      nsFilePicker* queuedPicker = (nsFilePicker*) data;
+      int16_t result;
+      queuedPicker->kdeFileDialog(&result);
+      if (queuedPicker->mCallback) {
+        queuedPicker->mCallback->Done(result);
+        queuedPicker->mCallback = nullptr;
+      } else {
+        queuedPicker->mResult = result;
+      }
+      queuedPicker->mRunning = false;
+      NS_RELEASE(queuedPicker);
+      return G_SOURCE_REMOVE;
+    }, this);
+
+    return NS_OK;
+  }
+
   NS_ConvertUTF16toUTF8 title(mTitle);
 
   GtkWindow* parent_widget =
       GTK_WINDOW(mParentWidget->GetNativeData(NS_NATIVE_SHELLWIDGET));
 
   GtkFileChooserAction action = GetGtkFileChooserAction(mMode);
 
   const gchar* accept_button;
@@ -575,16 +603,244 @@ void nsFilePicker::Done(void* file_choos
     mCallback->Done(result);
     mCallback = nullptr;
   } else {
     mResult = result;
   }
   NS_RELEASE_THIS();
 }
 
+nsCString nsFilePicker::kdeMakeFilter( int index )
+    {
+    nsCString buf = mFilters[ index ];
+    for( PRUint32 i = 0;
+         i < buf.Length();
+         ++i )
+        if( buf[ i ] == ';' ) // KDE separates just using spaces
+            buf.SetCharAt( ' ', i );
+    if (!mFilterNames[index].IsEmpty())
+        {
+        buf += "|";
+        buf += mFilterNames[index].get();
+        }
+    return buf;
+    }
+
+static PRInt32 windowToXid( nsIWidget* widget )
+    {
+    GtkWindow *parent_widget = GTK_WINDOW(widget->GetNativeData(NS_NATIVE_SHELLWIDGET));
+    GdkWindow* gdk_window = gtk_widget_get_window( gtk_widget_get_toplevel( GTK_WIDGET( parent_widget )));
+    return GDK_WINDOW_XID( gdk_window );
+    }
+
+NS_IMETHODIMP nsFilePicker::kdeFileDialog(PRInt16 *aReturn)
+    {
+    NS_ENSURE_ARG_POINTER(aReturn);
+
+    if( mMode == modeOpen && mFilters.Length() == 1 && mFilters[ 0 ].EqualsLiteral( "..apps" ))
+        return kdeAppsDialog( aReturn );
+
+    nsCString title;
+    title.Adopt(ToNewUTF8String(mTitle));
+
+    const char* arg = NULL;
+    if( mAllowURLs )
+        {
+        switch( mMode )
+            {
+            case nsIFilePicker::modeOpen:
+            case nsIFilePicker::modeOpenMultiple:
+                arg = "GETOPENURL";
+                break;
+            case nsIFilePicker::modeSave:
+                arg = "GETSAVEURL";
+                break;
+            case nsIFilePicker::modeGetFolder:
+                arg = "GETDIRECTORYURL";
+                break;
+            }
+        }
+    else
+        {
+        switch( mMode )
+            {
+            case nsIFilePicker::modeOpen:
+            case nsIFilePicker::modeOpenMultiple:
+                arg = "GETOPENFILENAME";
+                break;
+            case nsIFilePicker::modeSave:
+                arg = "GETSAVEFILENAME";
+                break;
+            case nsIFilePicker::modeGetFolder:
+                arg = "GETDIRECTORYFILENAME";
+                break;
+            }
+        }
+
+  nsAutoCString directory;
+  if (mDisplayDirectory) {
+    mDisplayDirectory->GetNativePath(directory);
+  } else if (mPrevDisplayDirectory) {
+    mPrevDisplayDirectory->GetNativePath(directory);
+  }
+
+    nsAutoCString startdir;
+  if (!directory.IsEmpty()) {
+    startdir = directory;
+  }
+  if (mMode == nsIFilePicker::modeSave) {
+    if( !startdir.IsEmpty())
+      {
+      startdir += "/";
+      startdir += ToNewUTF8String(mDefault);
+      }
+    else
+      startdir = ToNewUTF8String(mDefault);
+  }
+
+    nsAutoCString filters;
+    PRInt32 count = mFilters.Length();
+    if( count == 0 ) //just in case
+        filters = "*";
+    else
+        {
+        filters = kdeMakeFilter( 0 );
+        for (PRInt32 i = 1; i < count; ++i)
+            {
+            filters += "\n";
+            filters += kdeMakeFilter( i );
+            }
+        }
+
+    nsTArray<nsCString> command;
+    command.AppendElement( nsAutoCString( arg ));
+    command.AppendElement( startdir );
+    if( mMode != nsIFilePicker::modeGetFolder )
+        {
+        command.AppendElement( filters );
+        nsAutoCString selected;
+        selected.AppendInt( mSelectedType );
+        command.AppendElement( selected );
+        }
+    command.AppendElement( title );
+    if( mMode == nsIFilePicker::modeOpenMultiple )
+        command.AppendElement( "MULTIPLE"_ns );
+    if( PRInt32 xid = windowToXid( mParentWidget ))
+        {
+        command.AppendElement( "PARENT"_ns );
+        nsAutoCString parent;
+        parent.AppendInt( xid );
+        command.AppendElement( parent );
+        }
+
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::commandBlockUi( command, GTK_WINDOW(mParentWidget->GetNativeData(NS_NATIVE_SHELLWIDGET)), &output ))
+        {
+        *aReturn = nsIFilePicker::returnOK;
+        mFiles.Clear();
+        if( mMode != nsIFilePicker::modeGetFolder )
+            {
+            mSelectedType = atoi( output[ 0 ].get());
+            output.RemoveElementAt( 0 );
+            }
+        if (mMode == nsIFilePicker::modeOpenMultiple)
+            {
+            mFileURL.Truncate();
+            PRUint32 count = output.Length();
+            for( PRUint32 i = 0;
+                 i < count;
+                 ++i )
+                {
+                nsCOMPtr<nsIFile> localfile;
+                nsresult rv = NS_NewNativeLocalFile( output[ i ],
+                                      PR_FALSE,
+                                      getter_AddRefs(localfile));
+                if (NS_SUCCEEDED(rv))
+                    mFiles.AppendObject(localfile);
+                }
+            }
+        else
+            {
+            if( output.Length() == 0 )
+                mFileURL = nsCString();
+            else if( mAllowURLs )
+                mFileURL = output[ 0 ];
+            else // GetFile() actually requires it to be url even for local files :-/
+                {
+                nsCOMPtr<nsIFile> localfile;
+                nsresult rv = NS_NewNativeLocalFile( output[ 0 ],
+                                   PR_FALSE,
+                                   getter_AddRefs(localfile));
+                if (NS_SUCCEEDED(rv))
+                  rv = net_GetURLSpecFromActualFile(localfile, mFileURL);
+                }
+            }
+  // Remember last used directory.
+  nsCOMPtr<nsIFile> file;
+  GetFile(getter_AddRefs(file));
+  if (file) {
+    nsCOMPtr<nsIFile> dir;
+    file->GetParent(getter_AddRefs(dir));
+    nsCOMPtr<nsIFile> localDir(do_QueryInterface(dir));
+    if (localDir) {
+      localDir.swap(mPrevDisplayDirectory);
+    }
+  }
+        if (mMode == nsIFilePicker::modeSave)
+            {
+            nsCOMPtr<nsIFile> file;
+            GetFile(getter_AddRefs(file));
+            if (file)
+                {
+                bool exists = false;
+                file->Exists(&exists);
+                if (exists) // TODO do overwrite check in the helper app
+                    *aReturn = nsIFilePicker::returnReplace;
+                }
+            }
+        }
+    else
+        {
+        *aReturn = nsIFilePicker::returnCancel;
+        }
+    return NS_OK;
+    }
+
+
+NS_IMETHODIMP nsFilePicker::kdeAppsDialog(PRInt16 *aReturn)
+    {
+    NS_ENSURE_ARG_POINTER(aReturn);
+
+    nsCString title;
+    title.Adopt(ToNewUTF8String(mTitle));
+
+    nsTArray<nsCString> command;
+    command.AppendElement( "APPSDIALOG"_ns );
+    command.AppendElement( title );
+    if( PRInt32 xid = windowToXid( mParentWidget ))
+        {
+        command.AppendElement( "PARENT"_ns );
+        nsAutoCString parent;
+        parent.AppendInt( xid );
+        command.AppendElement( parent );
+        }
+
+    nsTArray<nsCString> output;
+    if( nsKDEUtils::commandBlockUi( command, GTK_WINDOW(mParentWidget->GetNativeData(NS_NATIVE_SHELLWIDGET)), &output ))
+        {
+        *aReturn = nsIFilePicker::returnOK;
+        mFileURL = output.Length() > 0 ? output[ 0 ] : nsCString();
+        }
+    else
+        {
+        *aReturn = nsIFilePicker::returnCancel;
+        }
+    return NS_OK;
+    }
+
 // All below functions available as of GTK 3.20+
 void* nsFilePicker::GtkFileChooserNew(const gchar* title, GtkWindow* parent,
                                       GtkFileChooserAction action,
                                       const gchar* accept_label) {
   static auto sGtkFileChooserNativeNewPtr =
       (void* (*)(const gchar*, GtkWindow*, GtkFileChooserAction, const gchar*,
                  const gchar*))dlsym(RTLD_DEFAULT,
                                      "gtk_file_chooser_native_new");
diff --git a/widget/gtk/nsFilePicker.h b/widget/gtk/nsFilePicker.h
--- a/widget/gtk/nsFilePicker.h
+++ b/widget/gtk/nsFilePicker.h
@@ -67,16 +67,22 @@ class nsFilePicker : public nsBaseFilePi
   nsString mDefaultExtension;
 
   nsTArray<nsCString> mFilters;
   nsTArray<nsCString> mFilterNames;
 
  private:
   static nsIFile* mPrevDisplayDirectory;
 
+  bool kdeRunning();
+  bool getKdeRunning();
+  NS_IMETHODIMP kdeFileDialog(PRInt16 *aReturn);
+  NS_IMETHODIMP kdeAppsDialog(PRInt16 *aReturn);
+  nsCString kdeMakeFilter( int index );
+
   void* GtkFileChooserNew(const gchar* title, GtkWindow* parent,
                           GtkFileChooserAction action,
                           const gchar* accept_label);
   void GtkFileChooserShow(void* file_chooser);
   void GtkFileChooserDestroy(void* file_chooser);
   void GtkFileChooserSetModal(void* file_chooser, GtkWindow* parent_widget,
                               gboolean modal);
 
diff --git a/xpcom/components/ManifestParser.cpp b/xpcom/components/ManifestParser.cpp
--- a/xpcom/components/ManifestParser.cpp
+++ b/xpcom/components/ManifestParser.cpp
@@ -38,16 +38,17 @@
 #include "nsTextFormatter.h"
 #include "nsVersionComparator.h"
 #include "nsXPCOMCIDInternal.h"
 
 #include "nsIConsoleService.h"
 #include "nsIScriptError.h"
 #include "nsIXULAppInfo.h"
 #include "nsIXULRuntime.h"
+#include "nsKDEUtils.h"
 
 using namespace mozilla;
 
 struct ManifestDirective {
   const char* directive;
   int argc;
 
   bool ischrome;
@@ -397,16 +398,17 @@ void ParseManifest(NSLocationType aType,
   constexpr auto kRemoteEnabled = u"remoteenabled"_ns;
   constexpr auto kRemoteRequired = u"remoterequired"_ns;
   constexpr auto kApplication = u"application"_ns;
   constexpr auto kAppVersion = u"appversion"_ns;
   constexpr auto kGeckoVersion = u"platformversion"_ns;
   constexpr auto kOs = u"os"_ns;
   constexpr auto kOsVersion = u"osversion"_ns;
   constexpr auto kABI = u"abi"_ns;
+  constexpr auto kDesktop = u"desktop"_ns;
   constexpr auto kProcess = u"process"_ns;
 #if defined(MOZ_WIDGET_ANDROID)
   constexpr auto kTablet = u"tablet"_ns;
 #endif
   // You might expect this to be guarded by MOZ_BACKGROUNDTASKS, but it's not
   // possible to have conditional manifest contents, so we need to recognize and
   // discard these tokens even when MOZ_BACKGROUNDTASKS is not set.
   constexpr auto kBackgroundTask = u"backgroundtask"_ns;
@@ -456,39 +458,44 @@ void ParseManifest(NSLocationType aType,
         CopyUTF8toUTF16(s, abi);
         abi.Insert(char16_t('_'), 0);
         abi.Insert(osTarget, 0);
       }
     }
   }
 
   nsAutoString osVersion;
+  nsAutoString desktop;
 #if defined(XP_WIN)
 #  pragma warning(push)
 #  pragma warning(disable : 4996)  // VC12+ deprecates GetVersionEx
   OSVERSIONINFO info = {sizeof(OSVERSIONINFO)};
   if (GetVersionEx(&info)) {
     nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", info.dwMajorVersion,
                               info.dwMinorVersion);
   }
+  desktop = u"win"_ns;
 #  pragma warning(pop)
 #elif defined(MOZ_WIDGET_COCOA)
   SInt32 majorVersion = nsCocoaFeatures::macOSVersionMajor();
   SInt32 minorVersion = nsCocoaFeatures::macOSVersionMinor();
   nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", majorVersion, minorVersion);
+  desktop = u"macosx"_ns);
 #elif defined(MOZ_WIDGET_GTK)
   nsTextFormatter::ssprintf(osVersion, u"%ld.%ld", gtk_major_version,
                             gtk_minor_version);
+  desktop = nsKDEUtils::kdeSession() ? u"kde"_ns : u"gnome"_ns;
 #elif defined(MOZ_WIDGET_ANDROID)
   bool isTablet = false;
   if (mozilla::AndroidBridge::Bridge()) {
     mozilla::AndroidBridge::Bridge()->GetStaticStringField(
         "android/os/Build$VERSION", "RELEASE", osVersion);
     isTablet = java::GeckoAppShell::IsTablet();
   }
+  desktop = u"android"_ns;
 #endif
 
   if (XRE_IsContentProcess()) {
     process = kContent;
   } else {
     process = kMain;
   }
 
@@ -583,25 +590,27 @@ void ParseManifest(NSLocationType aType,
     // When in background task mode, default to not registering
     // category directivies unless backgroundtask=1 is specified.
     TriState stBackgroundTask = (BackgroundTasks::IsBackgroundTaskMode() &&
                                  strcmp("category", directive->directive) == 0)
                                     ? eBad
                                     : eUnspecified;
 #endif
     int flags = 0;
+    TriState stDesktop = eUnspecified;
 
     while ((token = nsCRT::strtok(whitespace, kWhitespace, &whitespace)) &&
            ok) {
       ToLowerCase(token);
       NS_ConvertASCIItoUTF16 wtoken(token);
 
       if (CheckStringFlag(kApplication, wtoken, appID, stApp) ||
           CheckOsFlag(kOs, wtoken, osTarget, stOs) ||
           CheckStringFlag(kABI, wtoken, abi, stABI) ||
+          CheckStringFlag(kDesktop, wtoken, desktop, stDesktop) ||
           CheckStringFlag(kProcess, wtoken, process, stProcess) ||
           CheckVersionFlag(kOsVersion, wtoken, osVersion, stOsVersion) ||
           CheckVersionFlag(kAppVersion, wtoken, appVersion, stAppVersion) ||
           CheckVersionFlag(kGeckoVersion, wtoken, geckoVersion,
                            stGeckoVersion)) {
         continue;
       }
 
@@ -650,17 +659,17 @@ void ParseManifest(NSLocationType aType,
       }
 
       LogMessageWithContext(
           aFile, line, "Unrecognized chrome manifest modifier '%s'.", token);
       ok = false;
     }
 
     if (!ok || stApp == eBad || stAppVersion == eBad ||
-        stGeckoVersion == eBad || stOs == eBad || stOsVersion == eBad ||
+        stGeckoVersion == eBad || stOs == eBad || stOsVersion == eBad || stDesktop == eBad ||
 #ifdef MOZ_WIDGET_ANDROID
         stTablet == eBad ||
 #endif
 #ifdef MOZ_BACKGROUNDTASKS
         stBackgroundTask == eBad ||
 #endif
         stABI == eBad || stProcess == eBad) {
       continue;
diff --git a/xpcom/components/moz.build b/xpcom/components/moz.build
--- a/xpcom/components/moz.build
+++ b/xpcom/components/moz.build
@@ -66,16 +66,17 @@ LOCAL_INCLUDES += [
     "!..",
     "../base",
     "../build",
     "../ds",
     "/chrome",
     "/js/xpconnect/loader",
     "/layout/build",
     "/modules/libjar",
+    "/toolkit/xre",
 ]
 
 if CONFIG["MOZ_WIDGET_TOOLKIT"] == "gtk":
     CXXFLAGS += CONFIG["MOZ_GTK3_CFLAGS"]
     if CONFIG["MOZ_ENABLE_DBUS"]:
         CXXFLAGS += CONFIG["MOZ_DBUS_GLIB_CFLAGS"]
 
 if CONFIG["MOZ_BACKGROUNDTASKS"]:
diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -54,16 +54,17 @@
 #include "prproces.h"
 #include "nsIDirectoryEnumerator.h"
 #include "nsSimpleEnumerator.h"
 #include "private/pprio.h"
 #include "prlink.h"
 
 #ifdef MOZ_WIDGET_GTK
 #  include "nsIGIOService.h"
+#  include "nsKDEUtils.h"
 #endif
 
 #ifdef MOZ_WIDGET_COCOA
 #  include <Carbon/Carbon.h>
 #  include "CocoaFileUtils.h"
 #  include "prmem.h"
 #  include "plbase64.h"
 
@@ -2071,62 +2072,77 @@ nsLocalFile::SetPersistentDescriptor(con
 
 NS_IMETHODIMP
 nsLocalFile::Reveal() {
   if (!FilePreferences::IsAllowedPath(mPath)) {
     return NS_ERROR_FILE_ACCESS_DENIED;
   }
 
 #ifdef MOZ_WIDGET_GTK
-  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
-  if (!giovfs) {
-    return NS_ERROR_FAILURE;
-  }
+  nsAutoCString url;
 
   bool isDirectory;
   if (NS_FAILED(IsDirectory(&isDirectory))) {
     return NS_ERROR_FAILURE;
   }
 
+  nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (isDirectory) {
-    return giovfs->ShowURIForInput(mPath);
+    url = mPath;
   }
   if (NS_SUCCEEDED(giovfs->OrgFreedesktopFileManager1ShowItems(mPath))) {
     return NS_OK;
   }
   nsCOMPtr<nsIFile> parentDir;
   nsAutoCString dirPath;
   if (NS_FAILED(GetParent(getter_AddRefs(parentDir)))) {
     return NS_ERROR_FAILURE;
   }
   if (NS_FAILED(parentDir->GetNativePath(dirPath))) {
     return NS_ERROR_FAILURE;
   }
 
-  return giovfs->ShowURIForInput(dirPath);
+  url = dirPath;
 #elif defined(MOZ_WIDGET_COCOA)
   CFURLRef url;
   if (NS_SUCCEEDED(GetCFURL(&url))) {
     nsresult rv = CocoaFileUtils::RevealFileInFinder(url);
     ::CFRelease(url);
     return rv;
   }
   return NS_ERROR_FAILURE;
 #else
   return NS_ERROR_FAILURE;
 #endif
+  if(nsKDEUtils::kdeSupport()) {
+    nsTArray<nsCString> command;
+    command.AppendElement( "REVEAL"_ns );
+    command.AppendElement( mPath );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+  }
+
+  if (!giovfs)
+    return NS_ERROR_FAILURE;
+
+  return giovfs->ShowURIForInput(url);
 }
 
 NS_IMETHODIMP
 nsLocalFile::Launch() {
   if (!FilePreferences::IsAllowedPath(mPath)) {
     return NS_ERROR_FILE_ACCESS_DENIED;
   }
 
 #ifdef MOZ_WIDGET_GTK
+  if( nsKDEUtils::kdeSupport()) {
+    nsTArray<nsCString> command;
+    command.AppendElement( "OPEN"_ns );
+    command.AppendElement( mPath );
+    return nsKDEUtils::command( command ) ? NS_OK : NS_ERROR_FAILURE;
+  }
   nsCOMPtr<nsIGIOService> giovfs = do_GetService(NS_GIOSERVICE_CONTRACTID);
   if (!giovfs) {
     return NS_ERROR_FAILURE;
   }
 
   return giovfs->ShowURIForInput(mPath);
 #elif defined(MOZ_WIDGET_ANDROID)
   // Not supported on GeckoView