hello, this sounds like a problem possibly caused by adware on your pc. please go to ''firefox > 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]]

Thanks, Philipp. Malewarebytes and adwcleaner seems to have done the trick.