Hello andy4115, if you already try to rename(or delete) the cert8.db file in your profile folder don't continue to my reply.

1. Click the Windows Start button and copy the next bold %APPDATA%\Mozilla\Firefox\Profiles\ and paste it in the Search box at the bottom of the Start menu, without pressing Enter. A list of profiles will appear at the top of the Start menu.
2. Click on the profile with “default” in the name to open it in a window.
3. Find cert8.db file inside Firefox profile folder and rename the file to cert8.db.old (this will remove intermediate certificates that Firefox has stored).
4. Exit firefox and restart it.

• If that helped to solve your issue 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.

any luck?

thank you

Tried the above, no change I can't even load the Mozilla site, I get the "untrusted certificate" message. I can use Google Chrome, IE and Opera with no problem, but want Firefox back! Tried resetting the clock, that made no difference either......

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

Check out why the site is untrusted and click "Technical Details" to expand this section. If the certificate is not trusted because no issuer chain was provided (sec_error_unknown_issuer) then see if you can install this intermediate certificate from another source.

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 of the certificate.

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

If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".

• Note that some firewalls monitor (secure) connections and that programs like Sendori or FiddlerRoot can intercept connections and send their own certificate instead of the website's certificate.
• Note that it is not recommended to add a permanent exception in cases like this, so only use it to inspect the certificate.

time is OK and not the problem. On checking the certificate, it comes from ESET, which is my antivirus / firewall I have looked at my settings in ESET, but cannot see anything resembling SSL Any more ideas / help?

Try this:

• ESET Setup -> Advanced setup -> Web and email -> Protocol filtering -> SSL
• Certificates: Add the root certificate to known browsers

See also:

• SSL protocol: Do not scan SSL protocol

Tried both, and still no change.........

Is that certificate still issued by ESET when you disable this feature?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/