When Firefox web browser checks a security certificate, it also checks with the issuing authority if the certificate is valid. It appears that, near a certificate’s expiration date, the issuing authority may release a new certificate. The two certificates have conflicting expiration dates.

For reasons unknown, this caused Firefox to report a sec_error_revoked_certificate error and refuse to allow you to connect to the site!

To resolve this, presumably at the same time reducing the security of your browsing, complete the following:

For PC Users:

1. Open Firefox.
2. Go to Tools the top menu and select Options.
3. Click the Advance tab.
4. Click the following button:
   Encryption, then
   Certificates, then
   Validation
5. Check “Do not use OCSP for certificate validation.”
6. Click OK and restart Firefox.

For Mac Users:

1. Open Firefox.
2. Go to Firefox in the top menu and select Preferences.
3. Click the Advance button.
4. Click the following buttons:
   Encryption, then
   Validation
5. Un-check “Use the OCSP to confirm the validity of certificates.”
6. Click OK and restart Firefox.