Hello,

If you use Kaspersky, please see: https://support.mozilla.org/en-US/questions/1026631#answer-650916

For common troubleshooting steps for this issue, please see "This Connection is Untrusted" error message appears - What to do. It sounds like you may need to delete your cert8.db file and have Firefox recreate it; the steps are in the article.

Deleted cert8.db, restarted Firefox, error still present.

Do you have an antivirus or firewall software installed? If so, which one?

Security software with some form of web shield have caused this issue in Firefox, such as with Kaspersky. You will need to add their certificate into Firefox as they monitor secure (https) connections and send their own certificate instead of the website's certificate.

• (Example of how to add certificate) http://support.kaspersky.com/5414