I use both Firefox and IE, just depending on need, but I get lazy and usually run IE.
I only use IE for design compatibility purpose, so I just use the IEtab plugin for FireFox...all of the plugins negate the need to every use another browser.
I actually made the switch in preparation to change completely to Linux, which I still haven’t done yet. To get myself used to using Firefox, I edited the IE link on my quicklaunch to open FireFox instead. I’ve never looked back. :)