L'articolo l'ho letto (da Internet Explorer...) e consigliava il ripristino, che ho fatto senza risultato. di seguito quello che mi hai chiesto, grazie.
Mi dà lo stesso errore anche sulla webmail di libero.it
Codice di errore: SEC_ERROR_UNKNOWN_ISSUER
https://support.mozilla.org/L’autorità emittente del certificato del peer non è stata riconosciuta.
HTTP Strict Transport Security: false
HTTP Public Key Pinning: false
Catena di certificati:
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----