Obviously, firefox is the most used browser. It is so because of it's comfortablity and features which attract the people to get on it. First ie of microsoft was famous , but after the development of firefox , it has been the center of choice among all browser users. it have tabbing and selecting facility which is much expectable.
firefox is simply the best web browser on the Planet Earth and with its addons it could be much more than that
Firefox regularly increase popularity. IE and Firefox has approximatly same number of users currently but google chrome is fast than both.
I am using Firefox 3.5 but sometimes I wonder why its loading so slow unlike Chrome and IE?. But nonetheless I still like using firefox because of its add on and features which is really useful especially in SEO