<html class="reftest-wait"> <head> <script> function doTest() { var x = document.getElementById('TB_overlay'); x.style.display = 'block'; document.documentElement.removeAttribute('class'); } document.addEventListener("MozReftestInvalidate", doTest, false); </script> <style> #TB_window { border: 1px solid red; position: fixed; top: 0; left: 0; } #TB_overlay { height: 200px; left: 10px; position: fixed; top: 80px; width: 200px; display: none; opacity: 0.1; background-color: green; } </style> </head> <body> SOME CONTENT <div id="TB_overlay"> </div> <div id="TB_window"></div> </body> </html>