Bug 614993 - Assertion in the browser-chrome suite due to gPrivateBrowsingUI.uninit trying to remove its observers even if it hasn't registered them (ASSERTION: Oops! You're asking for a weak reference to an object that doesn't support that.: 'factoryPtr'); r,a=gavin

browser/base/content/browser.js

@@ -7457,6 +7457,7 @@ let gPrivateBrowsingUI = {
   _privateBrowsingService: null,
   _searchBarValue: null,
   _findBarValue: null,
+  _inited: false,
 
   init: function PBUI_init() {
     Services.obs.addObserver(this, "private-browsing", false);
@@ -7467,9 +7468,14 @@ let gPrivateBrowsingUI = {
 
     if (this.privateBrowsingEnabled)
       this.onEnterPrivateBrowsing(true);
+
+    this._inited = true;
   },
 
   uninit: function PBUI_unint() {
+    if (!this._inited)
+      return;
+
     Services.obs.removeObserver(this, "private-browsing");
     Services.obs.removeObserver(this, "private-browsing-transition-complete");
   },