<!DOCTYPE html> <html class="reftest-wait"> <body> <style> #a { border: 1px solid black; width: 100px; height: 100px; } #b { border: 1px solid blue; width: 50px; height: 50px; } div { position: absolute; } </style> <script> document.addEventListener("MozReftestInvalidate", function() { var a = document.querySelector("#a"); var b = document.querySelector("#b"); a.style.left = "10px"; b.style.left = "20px"; document.documentElement.removeAttribute("class"); }, false); </script> <div id="a"> <div id="b"> </div> </div> </body> </html>