Remember how there used to be so many annoying pop-up adds until pop-up blockers became popular. Well, the advertisng guys have come up with a new way to deliver pop-ups. They send them in on a port other than port 80. Lately, I have seen them on ports 82 and 90, and I expect it to get worse in the future. If you are getting a lot of pop-ups with a browser that should not be getting them, it is time to check your firewall rules.
Ad Filter for FF as well as Opera Ad Filter works out pretty good once you add the list of offending servers, but yes, if it is not in the list, you would have to deal with the annoying pop ups.
For good reasons, I will not give examples. Some might even be obvious. On the port 90 usage Kerio 2.15 gave a warning as ordinarily my browser is restricted to 80-82,443 and ports above 1023 (sometimes above 5000.) The site that used port 82 does it intermittently, to be extra sneeky. Also both are using pop-unders so you will not realize who sent you the browser window. The add filter for FF, would have to have the url's and I am willing to bet they change a lot. Anyone who wants to waste their time adding theindividual URL's to addblock, have fun. It sounds worse than looking at the adds to me. Recently I discontinued using addblock because of serious compatibility problems with parts of Yahoo. FF would crash unless Adblock was disabled in the extensions window. Turning if off within addblock did not work. I have been checking around and have found that Yahoo and other portals are working aggressively to get around addblock, and they are getting around the generic filters. Anyway, if you are getting pop-up and especially pop-under windows check your ports, that's all.