What security software do you have?

You usually see this notification if you have security software that wants to add its root certificate to Firefox to be able to hook in the internet connection and monitor your internet traffic. If this root certificate isn't installed then you get and SEC_ERROR_UNKNOWN_ISSUER error.

• https://support.mozilla.org/en-US/kb/error-codes-secure-websites

This question has been locked because the original author has deleted their account. While you can no longer post new replies, the existing content remains available for reference.