<!DOCTYPE html> <html class="reftest-wait"> <head> <title>Testcase Bug 851514</title> <style> #parent { position: fixed; height: 30px; width: 30px; background: green; left: 70px; top: 70px; overflow:hidden; display: none; /* So we can make sure there is only one frame construction and one reflow for the parent + child thing */ } #child { position: fixed; top: auto; left: auto; width: 10px; height: 10px; background: purple; } </style> <script> function doTest() { var par = document.getElementById("parent"); // Flush layout par.getBoundingClientRect(); par.style.display = "block"; document.documentElement.className = ""; } </script> </head> <body onload="doTest();"> <div id="parent"> <div id="child"></div> </div> The purple block should be inside the green block. </body> </html>