Firefox Developer Edition doesn't recognise Mkcert issuing authority

Hi,

I have been using Mkcert for a while now to provide HTTPS on a local machine (Ubuntu 21.04) and Firefox (89.0 (64-bit)) it was working ok but I started using Firefox Developer Edition (90.0b3 (64-bit)) and I get the error below (Mkcert is not a recognized authority).


> Someone could be trying to impersonate the site and you should not continue. Websites prove their identity via certificates. Firefox Developer Edition does not trust localhost:3000 because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates. **Error code: SEC_ERROR_UNKNOWN_ISSUER**

Is there some way around this? It works perfectly in regular Firefox but not in the developer edition for some reason.