<!DOCTYPE html>
<html class="reftest-wait">
<head>
<style type="text/css">
#float-blue {
 float: left;
 margin-right: 20px;
 background-color: blue;
 width: 40px;
 height: 100px;
}
.dyn {
 display: none;
}
.float-green {
 float: left;
 margin: 0 20px;
 background-color: green;
 width: 40px;
 height: 100px;
}
</style>
<script type="text/javascript">
function test() {
 document.getElementsByClassName('dyn')[0].style.display = 'block';
 document.documentElement.removeAttribute('class');
}
document.addEventListener('MozReftestInvalidate', test, false);
</script>
</head>
<body>
<div id="float-blue"></div>
<div class="float-green dyn"></div>
<div class="float-green"></div>
</body>
</html>