There isn't a set browser for the judging process. I judged websites for the NYC Regional last year, and that was one thing I checked, compliance on multiple browsers. But generally, if it's compliant with Firefox it should be compliant with IE, unless you have some odd-placed CSS code overriding something that SHOULD display. Someone else was talking to me about this the other day...
I do think it's important to make it compliant to IE, since I think the majority of the judges will probably use IE.
