Definitely Firefox is my browser of choice. In my opinion, its a lot more stable than IE and it has some awesome possibilites for adding to it. What comes stock with firefox that I absoultely love is the built in google search shortcut. Typing "g <search string>" in the URL bar will google search for your search string and bring you the results. Very nice
It also has similiar functions for dictionary.com and you can add your own search shortcut. Plus, it seems that a lot more people have been investing time into pointing out the flaws in IE and exploiting them (we know there are lots of them, come on... its M$, would you expect anything less? ) and firefox doesnt seem to have those massive amounts of bugs. But then again, I could be ignorant on that topic, I havent really done my research on flaws in firefox. But all in all, I prefer firefox over IE any day of the week.