I'm using Firefox ATM, but only because my iMac was somehow broken during a flight. It was wrapped in 10 layers of bubblewrap, they must have been throwing it against bulkheads. Anyway, I usually use Chrome. It's fast and easy to use.
I used to use Firefox but now I use Chrome. Nothing bad about Firefox though. Internet Explorer randomly pops up when I'm on Chrome. I'll never forgive you Internet Explorer!
Typically, it would depend on what I was doing to determine what browser I'd use. Usually, if I was just foruming/facebook'ing I'd use Firefox. Whenever gaming, I'd use Chrome.