I run FF 2 on one box and FF3 on another, for testing purposes. They have different "glitches", in that the same HTML/CSS/
JS will sometimes produce different results on the two versions. (I too get annoyed when the FF 2 installation keeps wanting to upgrade itself to FF 3 - I don't want it to do that, I've got it set up exactly how I need it thank you very much.)
Edit to add: oh, and some of the more horrible bugs in FF 2 are still there in FF 3.