Warning SSL_ERROR_BAD_CERT_DOMAIN because of an wrong port

We have an internal company website on Port 1443. Firefox shows an error message that the certificate is not valid for server.domain:1443. It would be only valid for server.domain But the certificate is valid and the issuer is installed as certificate authority. Other browsers like Edge and Internet Explorer trust this website and show no warning. Has someone an idea, what's wrong with the certificate?