hello Dejablue, first please make sure that the date, time & timezone are set correctly on your system. if this doesn't solve the issue (or it is already set properly), a possible solution depends on different factors:

• what is the error code shown under technical details on the error page?

in case the error code equals sec_error_unknown_issuer, please attempt to add an exception on the bottom of the error page in order to inspect the certificate like it is shown on the screenshot attached:

• which issuer information does the certificate contain?

please report back with those two pieces of information. thank you!

For these websites, FB Twitter and my bank there is no "Add exception" option. Some other sites do have that. The time/ time zone info is correct. The error code is: Error code: sec_error_expired_issuer_certificate

thank you, in this case please double-check that your system clock is set to the right date, time & timezone: time.is

if this doesn't help, you'd have to inspect the failing certificates closer because something isn't right on your system (maybe malware intercepting secure network traffic):please try

1. first enter chrome://pippki/content/exceptionDialog.xul into the address-bar
2. on the interface that opens enter "https://facebook.com" (or whichever particular url is failing to load) into the location server field.
3. click on get certificate & view and see who issued it

The link to Chrome didn't allow me access to Facebook, but I was able to see that the certificate is issued by: EasyTech, Expires on 10/15/2015. I have no malware because I ran Norton in Safe mode to totally clean my PC, then I scanned it with Windows Defender after that. This is a link to the certificate info: chrome://pippki/content/exceptionDialog.xul

Hey Phillipp, your link to inspect who issued the certificate was the key to the solution for me. When I responded with the issuer: Easy Tech, that reminded me of a program I d'loaded a long time ago. Sure enough, I deleted that program, and everything is back to normal...that is of course except for the years of bookmarks and stuff I've lost by trying to refresh Firefox. Thanks for your help!