Mozilla, Firebird and Konqueror all have options to block popups in their preferences dialogs.
To go another step, you can also install Privoxy, an ad-blocking web proxy.
I don't use Privoxy personally because I wish to allow non-popup banner ads to display. Sites like linuxquestions.org desperately need the ad money, and as long as the ads aren't too obnoxious (popups are too obnoxious) I'll tolerate them.
But that's just me.