<!DOCTYPE html> <html> <!-- https://bugzilla.mozilla.org/show_bug.cgi?id=507487 --> <head> <style> #content > * { display:block; width:100px; height:100px; background: purple; } #content > teST { display:block; width:100px; height:100px; background: green; } #content > test { display:block; width:100px; height:100px; background: blue; } </style> <script> function f() { document.getElementById('content').appendChild(document.createElementNS("test", "test")); document.getElementById('content').appendChild(document.createElementNS("test", "teST")); document.getElementById('content').appendChild(document.createElementNS("http://www.w3.org/1999/xhtml", "test")); document.getElementById('content').appendChild(document.createElementNS("http://www.w3.org/1999/xhtml", "teST")); } </script> </head> <body onload="f();"> <div id=content></div> </body> </html>