addblock plus doesn't do anything

I’d first check that Adblock Plus is actually enabled for the site. Click the Adblock Plus icon on the toolbar and make sure blocking isn’t disabled for that website. If it’s enabled and you’re still getting pop-ups, try Firefox’s Troubleshoot Mode to rule out another extension interfering. Also check Settings → Privacy & Security → Permissions → Block pop-up windows. One other thing: some ads are opened through notifications or new tabs rather than normal pop-up windows, so the fix can be different depending on what you’re seeing.