Recently, Mozilla Firefox users have been receiving full-screen ads promoting its paid open-source VPN service. These intrusive ads disable functionality of the web browser and cause browser unresponsiveness, forcing users to terminate the browser’s process. Users have shown their anger at the aggressive advertising from a company that claims to value user choice. Mozilla VPN is not available worldwide, only in selected regions. The advertisement has since been turned off by Mozilla after multiple reports were made on its bug tracking platform. A quick solution to disable the VPN ad is to toggle a button in Firefox’s advanced settings or use an ad blocker.
https://www.bleepingcomputer.com/news/security/mozilla-stops-firefox-fullscreen-vpn-ads-after-user-outrage/