Firefox for a few reasons...
Okay, the tabs, they are great.
But then you can also configure it to run faster, customize it with skins, it's stable, etc. All around a great browser.
Opera, why would anyone pay for a browser when there's so many free ones? idiots.
Netscape... Wow I remember when I first got on the web in... '96? lol
IE is just an advertisement in itself so many damn popups.
The bad thing with FF is some sites do not allow it.
So I do have an IE shortcut just in case.