<!DOCTYPE html>
<html class="reftest-wait">
<head>
<style type="text/css">
html, body {
 margin: 0; padding: 5px;
}
div {
 height: 20px;
 background-color: green;
}
#positive {
 margin-top: 30px;
 margin-bottom: 40px;
}
#negative {
 display: none;
 margin-top: -90px;
 background-color: blue;
}
</style>
<script type="text/javascript">
function test() {
 document.getElementById('negative').style.display = 'block';
 document.documentElement.removeAttribute('class');
}
document.addEventListener('MozReftestInvalidate', test);
</script>
</head>
<body>
<div id="positive"></div>
<div id="negative"></div>
</body>
</html>