Thank you! The jpberlin.de SSL wildcard certificate is issued by Thawte/digicert. I have imported it into eset's known certificate list. The issue persists.
For the www.jpberlin.de Web page, Firefox 68.0.1 also warns that "connection verified by a certificate issuer that is not recognized by Mozilla". The ESET certicate was imported into the Firefox certificate list, though. For now, it's just a warning...