Bug 24285. Disable FitToScreen(), which seems to be causing the problem.

xpfe/browser/resources/content/navigator.js

@@ -547,7 +547,7 @@ function createBrowserInstance()
   {
     //  TileWindow();
     // Make sure window fits on screen initially
-    FitToScreen();
+    //FitToScreen();
 	
     // Create the browser instance component.
     createBrowserInstance();