To be honest, like villej said, at least with Firefox updates come out almost instantly. There's also the advantage of being able to use it on a USB key, i.e. without registry - so you can use it properly on things like school PCs etc...link:
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johnhaller.com]
Lack of ActiveX controls is also good, but the best thing for me has to be extensions such as as the web developer tool, aardvark, and instant validation of html/xhtml etc...
Also, supports CSS-2 far better than I.E. 6 (which basically doesn't for all intents and purposes), and can handle true colour transparency in images, compared to 256-colour in IE. Very annoying that IE can't do that!
Basically, I love Firefox, and I doubt IE 7 will do anything to change my mind either
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