<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
xmlns:html="http://www.w3.org/1999/xhtml">
<vbox style="font-size:0" flex="1">
<box flex="1" />
<label style="font-size:16px" value="hello world" />
</vbox>
</window>