<html xmlns="http://www.w3.org/1999/xhtml"  
      xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
      style="opacity: 0.2;">
<head>
<script>

function x()
{
  document.documentElement.style.counterReset = "chicken";
  
  document.body.offsetHeight;
}

</script>
</head>

<body onload="setTimeout(x, 0);">Foo</body>

<xul:listbox/>

</html>