Bug 443493 – Unit test for Bug 331215 fails rather frequently on Mozilla2 builds

Test uses the thread manager to place a function on the event queue of the main
thread instead of using a timeout.
r=mconnor

toolkit/content/tests/chrome/bug331215_window.xul

@@ -69,7 +69,11 @@
         gBrowser.addEventListener("pageshow", onPageShow, false);
         gBrowser.loadURI("data:text/plain,latest");
       }
-      setTimeout(_delayedOnLoad, 1000);
+      let tm = Cc["@mozilla.org/thread-manager;1"].
+               getService(Ci.nsIThreadManager);
+      tm.mainThread.dispatch({
+        run: function() _delayedOnLoad()
+      }, Ci.nsIThread.DISPATCH_NORMAL);
     }
 
     function onPageShow() {