hello, this is scam as firefox will never display such alerts. this is an issue that may be caused by adware that is already on your pc though, so please take some precautions: #go to the firefox ''menu ≡ > addons > extensions'' & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). #also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there. #finally, run a full scan of your system with different security tools like the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes] & [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner], which are specialised in adware and browser hijackers. [[Troubleshoot Firefox issues caused by malware]]