For some reason just my IE CCleaner is working and will not clean my Firefox Mozilla files.....i have checked the settings and they seem to be ok. Though there might be something I was missing?
Is OP using ff3??? If so there are MANY MANY posts regarding CCleaner not cleaning FF# properly so please search the forum. AFAIK this has to do with the new manner (sqllite file) FF is handling it's Cookies, Temp data. It is my understanding that the Developers (of CCleaner) are currently working on getting FF3 to Clean correctly, until then my suggestion has been to use the built in erase private data.