Spyware Issue

I have this nasty Firefox spyware that opens pop-under ads in IE.  If I just browse in IE, no pop-under.  It only happens in Firefox.  I have both Spybot and Ad-Aware, but neither are picking this thing up.  Sugguestions?  Anyone having similar issues?  Has anyone walked a mile in my shoes and conquered this demon!?  HALP!?

Also, I have the official 4Chan Firefox extension.  Could this be what's causing the trouble?

Thanks, guys.

I uninstalled and reinstalled Firefox, and that didn't do squat.  I uninstalled IE7, but that still left IE6.  It turns out uninstalling that is a lot of trouble.  It needs to be repaired so the original setup/uninstall file is put back in place, and in order to do that I need my original XP CD which I currently don't have on me!  So right now, that's not an option.

I went in and commando-deleted a bunch of hidden cache and cookies left in IE6, but alas, I still have the pop-under.  I reinstalled IE7 'cause why the hell not, and yes, I still have the problems.

I'm gonna go in Rambo style and see if I can clear it myself, but as of right now, I've made mum progress in getting rid of this thing.  This is really pissing me off...