I'd say Firefox wins hands down... on the few occasions I have to use IE tab for awkward sites they always seem to load slower when using IE's engine.
Two FF functions I really like are:
1) The option to have Firefox restart with your previously opened tabs & windows.
2) The History function which not only stores your previously opened tabs, but also remembers the history of that particular tab... very useful if like me you're forever closing tabs absent-mindedly.