I'm surprised Firefox didn't warn me when I went to the page. Hostile teleco/MITM waiting for HTTP traffic are a real-world way that nation states deliver exploits.
It did for Librewolf -- what I moved to from Firefox. Self-Signed certs I'm down with, http I'm not, and never will be for any reason. Plain-text data transmissions have no acceptable reasoning.
You can pre-share the certificate out of band, or set up your browser to TOFU like SSH does. Then they are not useless and may be superior to PKI for certain threat models.