I have Firefox for Linux (I don't use Windows), but I honestly don't like it very much. I prefer Konqueror--it's faster than Firefox for me since I use KDE. I'd recommend Fx (Firefox) for people who use Windows, but not for Linux users who use KDE. I do keep Fx around because its Javascript is better than Konqueror's, but Konqeror is getting better and it has some nice features like highlighting misspelled words in text entry boxes, zoom buttons, Flash ad blocking, nice FTP browsing (shows it as icons rather than a list), and it passes the
Acid2 CSS test (Fx and IE fail it miserably). However, Konqueror is a Linux/Unix exclusive at the moment. Firefox takes an obscene amount of time to start for me--it takes about a minute or more to start on my (Linux) system, while Konqueror shows up in under 5 seconds.
Konq handles AD just fine, so I'm not worried about it.
That said, I do keep Fx around because Konqueror doesn't handle some sites properly like
www.aslpro.com that Firefox handles perfectly. (I can right-click the page in Konqueror, go to Open With, and select "Firefox" to open the page I'm on in Firefox if needed.) Thankfully, with the speed of Konqueror development, I'm finding myself turning to Fx less and less.