hello, this is a scam and sounds like a problem possibly caused by adware already on your pc. please 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). <br>also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there. <br>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]. [[Remove a toolbar that has taken over your Firefox search or home page]] [[Troubleshoot Firefox issues caused by malware]]

Thank you for the help. I rarely look at the add-ons but after checking, I found two that had managed to add themselves on. Got rid of them and ran adwcleaner and things seem to be back to normal. Once again, many thanks