Yes, your account won't get lost or such, they would just look into some private stuffs you had.
They will never be able to change your password though.
Thanks, I know that FireFox is a pretty useful browser when it comes to online protection. I actually got quite a few extensions, but not Firesheep. I don't think I will get it as I don't go on Facebook often. I also think I will get it just in case I do go on Facebook. I don't have anything personal on my facebook account, but I don't want to have the idea that it is hacked.