I tend to use firefox often, but use IE for uploading things cause I find its faster on my XP.
On my Vista, I just use IE cause I'm not on it enough to install stuff.

Firefox ofcourse! Since I changed, my computer's viruses have decreased by a half! Plus it's just so much faster... and I like the logo more! :D

I used Firefox until I got a Mac and now I use Safari. I sometimes still use Firefox if I'm trying to get on Painchat or something, but it's usually Safari.

Google Chrome, I was using firefox but it was stealing all my memory and causing my PC to lag. Thus far Chrome has proven to be much more speedy and less memory hungry.

I use IE and Google Chrome. I really like the incognito option in Chrome. It is also faster than IE. I also have XP. Vista is crap. I support software that is generally networked out and Vista is horrible about networking. Guess why Microsoft is coming out with Windows 7 so soon. Because Vista was so not what it was supposed to be. All that testing for what?