Sometimes, using AdBlock in Firefox may be too restrictive; by default, it blocks all ads, and you may just want to block the annoying ones: popups.
Firefox blocks them quite well, but it’s not perfect; some ad services have found ways to get around the blocker.
In this particular situation, I found that denying, in my Squid proxy server, the ad services which bypass the popup blocker, works very well.
This has the advantage of blocking them for a complete network, instead of just one PC, too. And it’s independent of browsers.
Popups are already annoying enough; to make them work around a popup blocker (which means that the user really doesn’t want to see them) is evil. So, the fact that these companies’ ads are blocked even before they get to the PCs is a nice bonus. 
Here’s my current list, which I block using dstdomain in squid.conf:
.zedo.com
.paypopunder.com
.t2t2.com
.profredirect.com
.dellonlinedirectly.com
.farssearch.net
.searchs123.com
.freefa.net
.clicksor.com
.paypopup.com
.adserver.com
.yieldmanager.com
.fastclick.net
.tribalfusion.com
Whenever I see a popup ad, I just add its domain to the list. As you can see, it’s not huge - Firefox works quite well.
Enjoy.
EDIT: I’m not included popups which Firefox 1.5.x does block, or any other kind of ads. I can live with those - if not, I’d be using AdBlock.
EDIT 2: I’ll be updating this post whenever I find new ones. I’ve already added 2 domains since I wrote this post.
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add the following expressions with squid guard
[/|\.|^]ad[s|v]?[/|\.]
[/|\.|^]ad[s|v]er.*[/|\.]
[/|\.|^]apfbanners/
[/|\.|^]banners?[/|\.]
/cgi-bin/nph-adclick/
[/|\.|^]clicktrack
[/|\.|^]event\.ng/
[/|\.|^]hittrack[/|\.]
[/|\.|^]httpads[/|\.]
[/|\.|^]phpads[/|\.]
[/|\.|^]smartbanner[/|\.]
[/|\.]sponsor[/|\.]
[/|\.|^]k5ads\.
[/|\.]falkag[/|\.]
[/|\.|^]fastclick[/|\.]
[/|\.|^]doubleclick[/|\.]
[/|\.|^]realmedia[/|\.]
Excellent!
I’ve set this up at home and at school and it’s worked grate!