--- /usr/lib/firefox/components/nsExtensionManager.js.orig	2006-10-12 05:13:10.000000000 +0200
+++ /usr/lib/firefox/components/nsExtensionManager.js	2006-10-12 05:28:20.000000000 +0200
@@ -3847,6 +3847,7 @@
       // 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]) {