I was curious about this because the release notes don't mention changing the behavior of HTTPS for localhost. I set up a local test and http://mytest.localhost

I was curious about this because the release notes don't mention changing the behavior of HTTPS for localhost. I set up a local test and http://mytest.localhost http://mytest.localhost works without having to add an entry to /etc/hosts, but https://mytest.localhost https://mytest.localhost with a self-signed TLS certificate will still raise a SEC_ERROR_UNKNOWN_ISSUER error. You still need to ignore those or install your own root CA with something like https://github.com/FiloSottile/mkcert https://github.com/FiloSottile/mkcert for that to work seamlessly.