I haven't used Windows in years, so I can't comment on that (other than, as others have said, IE is too deeply integrated into the OS to wipe, but you can at least let it gather dust as a web browser), but I've been using Firefox for some time now.
It wasn't the first tabbed browser I ever used -- I think that was Opera way back in the late 90s (well, actually, it wasn't tabbing, but it was a sort of precursor to tabbing) -- but the browser I was using before, Galeon, didn't have Firefox's extensions support, which is very VERY nice. I've gotten a lot of useful, and some not so much useful but still worth having, extra features out of extensions. One example is Session Saver, which means that I can close my Firefox window and then reopen it later to find the tabs I left still there (very useful when I want to free up the memory Firefox tends to slowly eat up, due to an odd misfeature). Another is a little extension that turns inline URLs (http, email addresses, etc.) that aren't coded as links into live links, which saves me a snarf 'n' barf. Things like that.
I recommend it highly. Oh, and there's one other thing I can add -- my wife, who was a Windows user until she moved in with me, used Firefox as part of her formula for keeping her PC virus/adware/spyware/malware/etc. free. So when I hook up Windows-using friends and relatives with Good Software, Firefox is one of the first things I set up.