Where is the popup displayed? Is it an ad for an ad blocker, or a message from the page saying you need to turn off an ad blocker? Could you test in Firefox's Safe/Troubleshoot Mode? In that mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem. ''If Firefox is running:'' You can restart Firefox in Safe/Troubleshoot Mode using either: * "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled) * (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled) and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button). ''If Firefox is not running:'' Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button). ''Note: Don't use the Refresh without first reviewing this article to understand what will be deleted:'' [[Refresh Firefox - reset add-ons and settings]]. Any improvement?