<html> <head> <title>Testcase bug - Crash [@ nsIFrame::IsThemed] when trying to get the computed style of a button in iframe</title> <style> iframe { width: 800px; height: 400px; } </style> </head> <body> This page should not crash Mozilla<br> <iframe id="content" src="data:text/html;charset=utf-8,%3Chtml%3E%3Chead%3E%3C/head%3E%3Cbody%3E%0A%3Cbutton%3E%3C/button%3E%0A%3C/body%3E%3C/html%3E"></iframe> <script> function getComputedStyles(){ var x=document.getElementById('content').contentDocument.getElementsByTagName('button')[0]; var style = document.defaultView.getComputedStyle(x, null).getPropertyValue('border-left-width'); } setTimeout(getComputedStyles,300); </script> </body> </html>