I’m a big fan of Firefox and its built-in popup blocker. But in recent weeks I’ve noticed an alarming trend: an increasing number of popups and pop-unders are slipping under the Firefox radar, and appear without warning on my screen.

I’m not along in noticing this. Quite a few people have had the same problem, and they’ve emailed me, asking if I know why this is happening, and how to stop it.

The answer, unfortunately, is no — I haven’t been able to find a fix, or even understand how these annoying windows manage to appear on my screen.

So I’m asking for your help. Do you know how these popups and popunders get by the Firefox popup blocker? More important still — how can I kill them? If you know the answers, or just have ideas, post a comment and let me and the world know.

Why are popups and popunders evading the Firefox popup blocker? If you know why, and how to fix it, let me know.