After some extremely bad customer service encounters with Tripadvisor yesterday (they gave me an unsolicited spam phone call, so I pulled up their site to complain and found that they have no customer service contact address), I discovered today that to add insult to injury, the *$%^-ing Tripadvisor pop-unders have caused Firefox to forget my saved session of 60+ tabs! I searched for how to block pop-unders, but all I found was how to block pop-ups, which I'm already doing according to Tools > Options. Can anyone here please tell me how I get rid of these wretched pop-unders and stop that ever happening again? Thanks.