Please consider turning on send info to Mozilla before posting a question. This helps us help you. As I have no info from your system that would help see things that cause issues. Please explain in complete detail is if telling someone that knows nothing.

I take it that we are to guess that ZA = something real important like maybe Zone Alarm ? Free or Paid ?

Have you set permissions in ZA to allow Firefox to go out ?

No idea what DV stands for : HP lap top Pavilion dv 7 Suggest checking for new drivers especially Network Drivers and Video card

https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

Note : Firefox 56.0.2 is current release https://www.mozilla.org/firefox/all/ Full Version Installer Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed.

Please let us know if this solved your issue or if need further assistance.

You can click the "Advanced" button to expand this section and show extra details. If the certificate is not trusted because no issuer chain was provided (SEC_ERROR_UNKNOWN_ISSUER) then click the blue error message to expand this section and show the certificate chain. You can click "Copy text to clipboard" and paste this base64 encoded certificate chain text in a reply. That will allow us to details like the issuer of the certificate.

• https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

• always be cautious when you get an 'Untrusted' error message
• never create a permanent exception without investigating the cause and only use this to inspect the certificate

Thanks for your reply, Pkshadow. I'll try to fill you in with as much as I know.

Yes. ZA is Zone Alarm. I run the free version.

Pavilion dv7 is the name Hewlett-Packard put on this model of laptop. I have no idea why that name.

Firefox is listed 14 times in Zone Alarm's Application Control list of programs. In all cases Trust Level is "Super". Outbound Trusted, Outbound Internet, Inbound Trusted, and Inbound Internet are all "allow".

I'll see if I can find how to turn on send info and try Firefox again.

This is the message I get -- for ANY web site

Your connection is not secure

The owner of us-mg6.mail.yahoo.com has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate.

Learn more…

Report errors like this to help Mozilla identify and block malicious sites

us-mg6.mail.yahoo.com uses an invalid security certificate.

The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported.

Error code: SEC_ERROR_UNKNOWN_ISSUER

If you use a bookmark then navigate to the web page starting with the main page or the sign in page in case there is a problem with this bookmark.

Note that you should avoid bookmarking a link with so many specific sub domains and possibly edit the link and remove the us-mg6 prefix.

• us-mg6.mail.yahoo.com => mail.yahoo.com