gecko/dom/tests/mochitest/chrome/focus_window2.xul

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin" type="text/css"?>

<window id="other-document"
        title="Focus Tests" onfocus="focused()"
        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

<script>
<![CDATA[

var gFocused = false;

function focused()
{
  if (window.arguments && !gFocused)
    setTimeout(function () window.arguments[0](window, window.arguments[1]), 0);
  gFocused = true;
}

]]>
</script>

<button id="other" label="OK"/>
<button id="other2" label="Cancel"/>

</window>