<!DOCTYPE html> <html class="reftest-wait"> <head> <style type="text/css"> #a { background-color: green; margin-bottom: 10px; height: 20px; } #b { background-color: green; margin-top: 20px; } #b div { display: none; height: 20px; margin-top: 40px; } </style> <script type="text/javascript"> function test() { document.getElementsByTagName('div')[2].style.display = 'block'; document.documentElement.removeAttribute('class'); } document.addEventListener('MozReftestInvalidate', test); </script> </head> <body> <div id="a"> </div> <div id="b"> <div></div> </div> </body> </html>