Sorry to hear that you are having issues with Firefox. We try to block untrusted connections for our users' safety, but sometimes Firefox makes mistakes. Is there a specific site(s) where this issue occurs? Something to double check, is that your operating system has the proper date, time and timezone settings configured. Having incorrect settings can lead Firefox to believe that a security certificate for a website is invalid. You can also view this Mozilla support article for more information about this warning message: *[["This Connection is Untrusted" error message appears - What to do]]