Recently I had to update an expired certificate for a web service. The only way to update the certificate was to log into the service and upload a new certificate. Unfortunately, the server folks implemented HSTS on the server so I had no choice but to use https to access the service. In Chrome, I was able to use the "thisisunsafe" easter egg to temporarily accept the old certificate while replacing it, but I was unable to find any workaround in Firefox that allowed me to log into the server, navigate to the administration menu, then upload and implement the new certificate.
Please go back to allowing users to decide when to override certificate errors.