As far as I can tell, this is a similar issue to one faced by Modernizr: Modernizr/Modernizr#224. In Element.js, the "Booleans" (lines 537-554) cause an exception to be thrown in IE9 when the media codecs aren't available. The solution is, I think to wrap this code in a try-catch block.
In my testing, this fixes the problem. I'll submit a pull request as well. My concern is that this may adversely impact performance, so perhaps a cleverer solution (which perhaps filters the "bools" array) would be in order...
please send us a fiddle or code that crashes ie9. well use them as
part of the specs
Here you go: http://jsfiddle.net/barryvan/Xf2mh/
IE's UA string is: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C)
This is Windows 7 Ultimate N (running in VirtualBox).