I use both Firefox and IE. I think IE is the better browser, but I do like Firefox because I can keep it stripped down to the bare minimum, so no shockwave or other plug-ins there.
I've used the Google toolbar for a couple of years now, and with SP-2 IE finally got the popup blocker it needed so I don't have the nightmares others will tell about.
Basically, I use Firefox for online shopping, reading the news, etc. and IE for fun.
bump