I can’t seem to find much that is good about the browser but here goes. For one, it seems to load pages faster than IE. That is a good thing. It also claims to be less prone to security flaws, that may be more because of its 6% market share compared to IE’s 92%. Who is going to write an exploit that can only reach 6%? Also good, it is much more strict to HTML standards than IE, although, a lot of pages out there break the rules and Firefox messes them up. Finally, there is tabbed browsing, its just nice.
Is it really better? I would say, no. Believe me, if I were running Linux or a MAC, I Firefox would probably be my browser, but on Windows, IE will probably win out. I plan to use Firefox daily for a while to get a better feel for it.