I am getting "Access Denied" responses this morning. Have tried "forget about this site" but i does not help. Still cannot get onto websites.
What site? Did you try Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#search
What security software are you running?
There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.