Why is Firefox 3 so problematic?
Asa’s blog reports that Firefox 3.0.11 was downloaded 150 million times in the 24 hours after release. Whilst you can find some other people with problems (such as in the comments of this Lifehacker post), it seems there’s no overall large issues with Firefox 3.0.11. If you’re having problems, try disabling some extensions and see if the problem is with one of them.