fix prefwindow js errors, r=hyatt

xpfe/components/prefwindow/resources/content/pref.xul

@@ -29,12 +29,13 @@
   function Startup()
     {
       hPrefWindow = new nsPrefWindow('panelFrame');  
+      hPrefWindow.init();
       
       if( !hPrefWindow )
         throw "failed to create prefwindow";
 
-      <!-- If this call worked, we could center the window here: -->
-      <!-- centerWindowOnScreen(); -->
+      // If this call worked, we could center the window here:
+      // centerWindowOnScreen();
       
       // modify the cookie tree entry if imageblocking is disabled. 
       if( hPrefWindow.getPref( "bool", "imageblocker.enabled" ) )