Another Firefox user here, pop-up free for 1 year, feel the Mozilla love!
Of course, if you have Windows XP service pack two, it includes an update to Internet Explorer which can block pop-up ads.
I would stay away from add on tools that say they will block pop-ups; while some may be legit there are others that will just put spyware and adware on your system.
Cheers,
Psilo