Added release of throbber in the hopes that this would allow the image

group and hence the image manager to be released, but it doesn't quite do
the trick because the ref count of the throbber is 2...

webshell/tests/viewer/nsBrowserWindow.cpp

@@ -322,6 +322,9 @@ nsBrowserWindow::Destroy()
     mWebShell->Destroy();
     NS_RELEASE(mWebShell);
   }
+
+  NS_IF_RELEASE(mThrobber);
+  // XXX What about releasing all the other objects...
 }
 
 void