<?xml version="1.0"?> <?xml-stylesheet href="chrome://global/skin" type="text/css"?> <window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" orient="vertical"> <label value="The iframe below should show the string 'Here'"/> <iframe src="data:application/vnd.mozilla.xul+xml,<window xmlns='http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul'><label value='Here'/></window>" style="display: none" onload="this.style.display = ''"></iframe> </window>