I am running Firefox 7.0.1 and Thunderbird 7.0.1 on Mac OS X 10.6.8.

I was exploring/nosing around their Preferences, and deleted many Authorities in the Certificate Manager.

Afterwards I started to get lots of messages from Firefox and Thunderbird that looks like this:

[domain ...:443] uses and invalid security certificate.

The certificate is not trusted because the issuer certificate is not trusted.

(Error code: sec_error_untrusted_issuer)

There are only two buttons I could click on: "View Certificate" and "Cancel". Regardless of which one I choose, the messages repeatedly pop up whenever I load a webpage.

Interestingly, I even have trouble logging onto websites (Gmail, superuser, etc.) even on other browsers on other computers. For instance, when browse to superuser.com, I am logged in. But when I ask a question, I am asked to log in, yet I can't log in with my Google Account (which I always use for stackexchange sites).

I don't even know how to troubleshoot this problem, or if there is some way to reset my system's certificate information?

This is really weird, and impedes my normal web browsing.


I looked up your error in regards to Firefox, and found this solution:

  1. Type the phrase about:support as a URL in the Firefox address bar.
  2. Click the button next to Profile Directory labeled "Open Containing Folder". That will launch Windows Explorer.
  3. Close Firefox.
  4. Locate the file cert8.db in the Windows Explorer pane you opened in step 2 and move the file to a different location (like your desktop) or rename it.
  5. Start Firefox again.

This will clear the file out and should resolve the errors you are getting.

  • 1
    This worked! The relevant folder for Thunderbird can be found here: kb.mozillazine.org/Profile_folder_-_Thunderbird , there is also a cert8.db file in there that you should remove to achieve the same effect. Thanks for the answer! – hpy Oct 10 '11 at 16:55
  • By the way I had two .db files under ~/.mozilla/firefox/{Profile}/ I had to move both of them – chamalabey Dec 7 '18 at 4:35

For Thunderbird, you can click on Help then Troubleshooting information. Then click Show Folder next to Profile Folder. Just right click and rename the cert8.db, or cert8, to cert8ORIG. Then reopen TB. You might have to accept certificate exceptions for some mail services, but it will remember them for the future.


On top of deleting or renaming cert8.db in your Firefox profile folder, it's probably a good idea to delete or rename cert_override.txt as well.

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