As per here Few days ago (after an update) FF simply refused to accept my self-signed certificate anymore, Firefox requires SAN (Subject Alternative Names) present:
It must be due to removed "subject common name" fallback support from certificate validation. This fallback mode was previously enabled only for manually installed certificates. The CA Browser Forum Baseline Requirements have required the presence of the "subjectAltName" extension since 2012, and use of the subject common name was deprecated in RFC 2818. Firefox from 101.0 onward no longer use certificate CN (Common Name) for matching domain name to certificate and have migrated to only using SAN (Subject Alternate Name) so if you self sign for internal devices you’ll need to regenerate.