Bug 497844, use focus event instead of load event, r=gavin

toolkit/content/tests/chrome/window_panel_focus.xul

@@ -3,7 +3,7 @@
 <?xml-stylesheet href="chrome://mochikit/content/tests/SimpleTest/test.css" type="text/css"?>
 
 <window title="Panel Focus Tests"
-  onload="setTimeout(showPanel, 0)"
+  onfocus="setTimeout(showPanel, 0)"
   xmlns:html="http://www.w3.org/1999/xhtml"
   xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">