Firefox takes like 3 times longer to load anything than IE. And I can't figure out why. That said, I use both equally, depending on what I need to do. If it's speed, I use IE. If it's something that breaks IE (like any site that uses the <EMBED> tag), I use FF.
Although, I have Firefox re-named "FYREFOKS" on my desktop to mock the legions of "IF U DOTN UZE FYREFOKS U R STUIPD N SOULLD DAI" morons who seem to swarm, like, every forum ever made.
Though, if it's any consolation, I have IE re-named "Internet Exploder".