What security software do you have?

Did you check issuer of the certificate?

You can check the date and time and time zone in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

• https://support.mozilla.org/kb/Security+Connection+Failed

If you can't inspect the certificate via "I Understand the Risks" then try this:

Open the "Add Security Exception" window by pasting this chrome URL in the Firefox location/address bar and check the certificate:

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

In the location field of this window type or paste the URL of the website.

• retrieve the certificate via the "Get certificate" button
• click the "View..." button to inspect the certificate in the Certificate Viewer

You can inspect details like the issuer and the certificate chain in the Details tab of the Certificate Viewer. Check who is the issuer of the certificate. If necessary then you can attach a screenshot that shows the certificate viewer.

I have ESET Nod32 and MBAM. I have disabled both and refreshed the page but this made no different. Also I don't have a problem with Chrome.

It says it expires in September of 2017. And this isn't the only certificate affected, some other sites have the same issue.

You can check the date and time and time zone in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

• https://support.mozilla.org/kb/Secure+Connection+Failed

The date, time, and time zone all seem to be correct (1/3/2016, 9:13PM)

The link you posted gives me a page not found.

(I fixed the link)

Try to rename the cert8.db file (cert8.db.old) and delete the cert_override.txt file in the Firefox profile folder to remove intermediate certificates and exceptions that Firefox has stored.

If that has 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 previously stored 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 current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

I closed FF, renamed the cert8.db file and deleted the cert_override.txt file, and then restarted FF but no success. I then restored the old cert8 file.

I tried to completley forget about all mozilla sites and then revisited https://addons.mozilla.org/en-US/firefox/ but the same problem occurred. I tried a few other sites with the same results.

I've backed up all my FF data at this point so if a wipe of FF of any kind would help I am willing to go that route.

I used revo uninstaller to completely remove Mozilla Firefox. I then reinstalled Firefox and the problem persisted. Anything else I can do to wipe it without a complete OS reinstall?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10