Asa Dotzler – Firefox and more: blocking those flash pop-unders with firefox
privacy.popups.disable_from_plugins

It seems like advertising agencies never stop looking for ways to force their products on us. I had begun to notice some sites exploiting what I thought was a bug in Firefox’s JavaScript engine to generate pop-ups. Turns out they’re using flash to spawn the new window. Thankfully there’s a way to stop it, but you may run into problems with some sites. Works great for me so far… give it a try and see what you think.