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

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

<window id="other-document"
        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

<script type="application/javascript"
        src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>

<script>
<![CDATA[

function focused()
{
  if (window.arguments)
    setTimeout(function () window.arguments[0](window, window.arguments[1]), 0);
}

SimpleTest.waitForFocus(focused);

]]>
</script>

<button id="other" label="OK"/>
<textbox id="other-textbox" value="test"/>

</window>