Fix Invalid Certificates Error in Mozilla Firefox

When you connect to websites over a secure connection (HTTPS), the connection is encrypted using a security certificate issued by one of the certificate issuing authorities like Comodo, GoDaddy, Verizon, Symantec, Digicert etc. But if there is some problem with the certificates downloaded from these websites or if they cannot be verified, then Firefox will refuse to connect to the websites trying to use such certificates. While there could be problem in the certificate configuration on the web server itself, these errors in Firefox could also result from some local Firefox certificate database corruptions.

First thing you should check is the system date. If the date and time is not correct in your PC, then Firefox will be verifying the certificates using a wrong date and will give errors. You can correct the date manually, or you can use our UpdateTime tool to automatically update the date and time from NTP servers.

Fix Corrupt Certicate Error in Firefox

If correcting the system time does not fix the problem, then perhaps it is possible that the certificates store database in your Firefox profile has become corrupt. You can then fix the certificate database in this way:

  1. Press the Alt key on your keyboard to make the menubar visible in Firefox. Then select Help → Troubleshooting Information from the menubar.Fix Corrupt Certicate Error in Firefox
  2. On the troubleshooting page in Firefox, scroll down and click on the Show Folder button to open your default Firefox profile folder.Fix Corrupt Certicate Error in Firefox
  3. When the Firefox profile folder opens up, close all the Firefox browser windows and wait for ten seconds to let the Firefox processes to be terminated.
  4. In the Firefox profile folder, locate a file named cert8.db or cert9.db and delete it.Fix Corrupt Certicate Error in Firefox
  5. Restart Firefox. This will recreate the cert8.db or cert9.db file once again and now you should not have any security certificates related errors.

If you still get the problem, then perhaps it is your antivirus software’s web scanning module that is intercepting the secure connection to websites. In this case, you will see the problem in all web browsers – not only in Firefox. You can either disable web scanning (also called HTTP/HTTPS scanning) in your antivirus software, or you can add the exception to the antivirus’s local secure certificate by clicking on the Add Exception button on the Firefox’s invalid certificate warning page. Before you add the exception make sure that the certificate is from your antivirus software. You can also consult your antivirus vendor for more help.

Firefox is very security focused  web browser and won’t let you connect to a web site if it is using an invalid security certificate. But the certificates could also be detected as invalid owing to some local system problems, and you can easily fix them using the steps described above.


  1. Deleted cert8.db and it was not recreated. Is this file essential? There is a cert9.db -would this be the file for a more recent version?
    I discovered that the problem in my case was being caused by BitDefender and had to disable ‘Encrypted web scan’ to fix it.

    1. Yes cert9.db is for the new version of Firefox. You are right antivirus HTTP/HTTPS or web scanners can cause this problem. But disabling web scanning will make your system insecure. Instead, you can add Bitdefender to your trusted certificate list in Firefox.

Comments are closed.