Hi ! You probably didn't install a VARNA theme, or you would have mentioned it. Your system details show an add-on that you more than likely didn't install either ('Start 1.1') - I think it's safe to say that you may have malware. Go to the 3-bar menu (or 'Tools') => Addons => Extensions and look for any unfamiliar or suspicious looking extensions. When you find any : remove them. Do the same in Windows Control Panel. However : most malware will be 'hiding' somewhere , so let's run malware scans : Further information can be found in this article : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no Run most or all of the listed malware scanners. They all work differently - what one program doesn't pick up, the other might.