Those pop-ups are definitely scam-ware, NOT Amazon pop-ups. Look at them carefully, they are some jokers who will try to get your personal information and then spam you mercilessly all for the promise of maybe sending you a gift card. They do that while pretending to be Amazon, or WalMart, or a dozen other companies--none of whom know anything about these scams.
The pop-ups are probably coming in because the forum is probably accepting ads from a broker
, who in turn has no idea what code is in those ads (they can change after they've been booked) so no one really has any control over what shows up. Except you, who can disable all that stuff, and accept the collateral damage. (Which isn't much.)