SSL problem with Firefox; no problem with Safari or Chrome
I have a website development system with SSL enabled for testing. The certificate is self-signed but expired. I added a new self-signed certificate. When I load a development website, Firefox issues a Warning: Potential Security Risk Ahead. When I click Advanced, the error is SSL_ERROR_BAD_CERT_DOMAIN, with additional information that the certificate has expired. Clicking Accept Risk and Continue loads an ISP website with network details of attached devices. I have repeatedly cleared Firefox cached and saved data by clearing recent history, followed by clearing everything for all the check boxes on the page. I have examined the certificates in the security settings, view certificates. The expired certificate is listed. After deleting the expired certificate from the list, and loading the development website again, results in the same problem all over again.
I have no problem with Safari or Chrome browsers, only Firefox. Firefox 76.0.1, Mac OS 10.14.6. MAMP based development system, version 5.7 using Apache.
How can I delete the expired certificate so it stays deleted, and make Firefox use the new certificate?