<!DOCTYPE HTML> <html class="reftest-wait"> <head> <script> function doTest() { var d = document.getElementById("d"); d.style.opacity = 0.5; document.documentElement.removeAttribute("class"); } window.addEventListener("MozReftestInvalidate", doTest); </script> </head> <body> <div id="d" style="width:100px; height:100px; background:blue;">Hello</div> </body> </html>