See: *https://support.mozilla.org/en-US/kb/disable-or-remove-add-ons *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Hello r.iozzo, That "From Doc To PDF" is (as you probably already suspected) a browser hijacker, that you of course will want to get rid of. Go to the Firefox menu (≡) => Options => Add-ons => Extensions and remove anything that looks unfamiliar or suspicious. Do the same in Windows Control Panel => Programs. Next step is to run malwarescans - 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. Also see : https://malwaretips.com/blogs/remove-fromdoctopdf-by-myway/