Try to rename the cert8.db file in the Firefox profile folder to cert8.db.old or delete the cert8.db file to remove intermediate certificates that Firefox has stored.

If that helped to solve the problem then you can remove the renamed cert8.db.old file.
Otherwise you can rename (or copy) the cert8.db.old file to cert8.db to restore the previous intermediate certificates.
Firefox will automatically store intermediate certificates when you visit websites that send such a certificate.

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder

Thanks for the fast reply, cor-el. Unfortunately, that didn't work.

Additional info: I tried clicking on Add Exception on the Untrusted Connection warning page. In the dialog box under Certificate Status, it said Valid Certificate. I clicked on the View button and at the top of the box it said that it could not verify this certificate for unknown reasons. I clicked on the Details tab and saw that only www.e-zpassny.com was shown under Certificate Hierarchy. I thought that was odd because I noticed that there's more to the hierarchy when I viewed the certificate under my Vista administrator account. Specifically, GeoTrust Global CA should be there. Do I need to reinstall Firefox?

Did you check who issued the certificate?

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 intermediate certificates that are used in the Details pane.

I edited my previous post with more details. Please check it out.

It was issued by GeoTrust DV SSL CA and is valid from 1/12/12 to 3/14/15. Also, I noticed that if I tried to go to https://e-zpassny.com again or reload the page, then click on Add Exception and under Certificate Status it says: This site attempts to identify itself with invalid information. Unknown Identity Certificate is not trusted because it hasn't been verified by a recognized authority. However, when I click on Get Certificate, the Certificate Status changes to Valid Certificate. ???

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't click the Reset button on the Safe mode start window or otherwise make changes.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Tried safe mode and that didn't work. Tried disabling all extensions and that had no effect. Although, very briefly, I saw the e-zpass page load, but then the error message returned. Re-enabled each extension one at a time and that didn't work either. I tried duplicating my actions to try to make that brief appearance happen again, but I couldn't do it.

It seems to have resolved itself now. Beats me why.