If you expand the "Technical Details" part of the certificate error page, could you copy/paste that section into a reply? In particular, there is a code at the end in parentheses that may be helpful in figuring out the problem.

Does this problem occur with any other secure sites?

this is the error message I get

mylu.liberty.edu uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. (Error code: sec_error_unknown_issuer)

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"
• Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate"
• Click the "View" button and inspect the certificate and check who is the issuer.

You can see more details like the intermediate certificates that are used in the Details tab.

If that isn't possible then open this chrome URL by pasting or typing this URL in the location/address bar to open the "Add Security Exception" window and check the certificate:

• chrome://pippki/content/exceptionDialog.xul

In the location field type/paste the URL of the website

• retrieve the certificate via the "Get certificate" button
• inspect the certificate via the "View..." button