Firefox doesn't have any sort of built-in ad blocking functionality, whether in the release version or Aurora. The built-in pop-up blocker only prevents certain types of pop-up windows from opening; it doesn't close windows that have opened. * [[Pop-up blocker settings, exceptions and troubleshooting]] What you describe is probably the pop-up blocking in Adblock Plus. Ad pop-up windows that get by Firefox's built-in pop-up blocker are automatically closed. Supposedly, this happens so quickly that no connection to the ad server is made. And yes, once those windows are closed, they're really closed. * https://adblockplus.org/blog/on-the-pop-up-blocker-in-adblock-plus