Download Firefox 12-51 52 Esr Updated -

This is expected. Modern HTTPS standards (TLS 1.3) and certificate authorities often reject Firefox 12-51. You can try enabling older TLS versions in about:config ( security.tls.version.enable-deprecated ), but this is a security risk.

Will this browser need to access the or just a local network ? Download Firefox 12-51 52 Esr