hello roglyn, multiple other affected users have reported that this was an issue caused by malware on their pc. please run a full scan of your system with the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes] and [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner] and see if they get any results. [[Troubleshoot Firefox issues caused by malware]]