References:
https://bugzilla.novell.com/show_bug.cgi?id=217374
https://bugzilla.mozilla.org/show_bug.cgi?id=356370

Index: toolkit/mozapps/extensions/src/nsExtensionManager.js.in
===================================================================
RCS file: /cvsroot/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in,v
retrieving revision 1.144.2.60
diff -u -p -6 -r1.144.2.60 nsExtensionManager.js.in
--- toolkit/mozapps/extensions/src/nsExtensionManager.js.in	17 Sep 2006 22:17:11 -0000	1.144.2.60
+++ toolkit/mozapps/extensions/src/nsExtensionManager.js.in	29 Nov 2006 07:54:31 -0000
@@ -4008,12 +4008,13 @@ ExtensionManager.prototype = {
     for (var i = 0; i < allItems.length; ++i) {
       var item = allItems[i];
 
       // An item entry is valid only if it is not disabled, not about to 
       // be disabled, and not about to be uninstalled.
       var installLocation = this.getInstallLocation(item.id);
+      if (! installLocation) continue;
       if (installLocation.name in StartupCache.entries &&
           item.id in StartupCache.entries[installLocation.name] &&
           StartupCache.entries[installLocation.name][item.id]) {
         var op = StartupCache.entries[installLocation.name][item.id].op;
         if (op == OP_NEEDS_INSTALL || op == OP_NEEDS_UPGRADE || 
             op == OP_NEEDS_UNINSTALL || op == OP_NEEDS_DISABLE)