It's a 1990s revival, as the intrusive world of pop-up ads fights its way back through your defenses...
You may have noticed that a lot of sites are managing to launch pop-up windows that can penetrate any standard blocker built into a web-browser these days, and pretty much all proprietary blockers too. What's going on? The innovation creeping in to return us to the God-awful 1990s is Adimpact, which charges its clients a rolling fee to feed DHTML-based pop-ups to their sites. There seems little protest around on the web, though a quick search will find various PRs and sellers eulogising the technology. Adimpact was launched in 2006, but seems to have finally attracted some higher-profile clients such as the IMDB.
Maybe it's a combination of things: what sites are visited; Firefox; and Kerio firewall...but I can't remember the last time I saw a pop-up on this bugger!
One good thing with Firefox is that you can add on extensions like Ad Blocker and No-Script. I particularly like No-Script, as this is one way that hackers can get into your system fast.