I just updated my Unibody 15" MBP (only 2GB RAM) and now firefox is consistently using over 500MB of memory. It really seems to be clogging things up. Anyone else seeing this?
EDIT: Now 640mb. wtf.
EDIT: 830MB when playing youtube. come one.. .
Try quitting Firefox then starting it up in safe mode (which does not load any extensions) and then seeing if the growth continues like crazy. If it doesn't, then odds are one of your extensions is contributing to a nasty memory leak.
To run it in safe mode on MacOS X:
http://kb.mozillazine.org/Safe_mode#Mac_OS_X