Index: toolkit/mozapps/extensions/src/nsExtensionManager.js.in
================================================================================
--- toolkit/mozapps/extensions/src/nsExtensionManager.js.in
+++ toolkit/mozapps/extensions/src/nsExtensionManager.js.in
@@ -119,6 +119,7 @@
 
 const KEY_APP_PROFILE                 = "app-profile";
 const KEY_APP_GLOBAL                  = "app-global";
+const KEY_APP_SYSTEM                  = "app-system";
 
 const CATEGORY_INSTALL_LOCATIONS      = "extension-install-locations";
 
@@ -2676,6 +2677,16 @@
                                                      priority);
   InstallLocations.put(profileLocation);
 
+  // Register App-System Install Location
+  try {
+    var appSystemExtensions = getDirNoCreate("DrvD", ["usr","lib","browser-extensions","firefox"]);
+    var priority = nsIInstallLocation.PRIORITY_APP_PROFILE - 1;
+    var systemLocation = new DirectoryInstallLocation(KEY_APP_SYSTEM,
+                                                      appSystemExtensions, true,
+                                                      priority);
+    InstallLocations.put(systemLocation);
+  } catch (e) {}
+
 #ifdef XP_WIN
   // Register HKEY_LOCAL_MACHINE Install Location
   InstallLocations.put(
@@ -3852,7 +3863,7 @@
 
     // Prepare themes for installation
     // Only enumerate directories in the app-profile and app-global locations.
-    var locations = [KEY_APP_PROFILE, KEY_APP_GLOBAL];
+    var locations = [KEY_APP_PROFILE, KEY_APP_GLOBAL, KEY_APP_SYSTEM];
     for (var i = 0; i < locations.length; ++i) {
       var location = InstallLocations.get(locations[i]);
       if (!location.canAccess)
@@ -3918,7 +3929,8 @@
       var items = PendingOperations.getOperations(OP_NEEDS_INSTALL);
       for (i = items.length - 1; i >= 0; --i) {
         if (items[i].locationKey == KEY_APP_PROFILE ||
-            items[i].locationKey == KEY_APP_GLOBAL)
+            items[i].locationKey == KEY_APP_GLOBAL ||
+            items[i].locationKey == KEY_APP_SYSTEM)
           itemsToCheck.push(items[i].id);
       }
       this._finishOperations();
@@ -4903,7 +4915,8 @@
       }
     }
     else if (installLocation.name == KEY_APP_PROFILE ||
-             installLocation.name == KEY_APP_GLOBAL) {
+             installLocation.name == KEY_APP_GLOBAL ||
+             installLocation.name == KEY_APP_SYSTEM) {
       // Check for a pointer file and remove it if it exists
       var pointerFile = installLocation.location.clone();
       pointerFile.append(id);