I have a MBP (2.16 3Gb ram) and on two occasions in the past few weeks, i have been using FF 3.01 and the cpu usage was in the 90%-110% and the computer woudl heat up to the 140-150 F degree range and the fans would go on high and what not. This only happens it seems like on certain sites, and randomly (not on the same site again if you restart the app). I want to make sure this is not a hardware issue and just a FF or particular site issue. Last night it happened when i was on www.iminlikewithyou.com thanks
It's an Adobe have written a bad Flash plugin issue. You just have to put up with it, or go pester Adobe, but they don't seem to listen.
try new adobe flash 10 beta 2, it offers much improved performance, if you don't mind its beta status.