Firefox uses an invalid security certificate. The certificate is only valid for Firefox.blog. I get this message when I click on Firefox News.
Solved! Go to Solution.
You may have a problem with an intermediate certificate that Firefox has stored.
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.
If that didn't help then remove or rename secmod.db (secmod.db.old) as well.
You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.
Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".
You can see more Details like intermediate certificates that are used in the Details pane.