<!DOCTYPE html>
<html class="reftest-wait">
<body>

<div id="empty" style="position:fixed; z-index: 4; left:200px; top:200px; width: 0px">
  <div style="position:fixed; width:400px; height: 400px; background-color:green; top: 200px; left: 200px"></div>
</div>
<div style="width:400px; height: 400px; background-color:blue"></div>

<script>
  function doTest() {
    document.getElementById("empty").style.left = "201px";
    document.documentElement.removeAttribute("class");
  }
  document.addEventListener("MozReftestInvalidate", doTest);
</script>
</body>
</html>