Repro:
Attempt to log in via minecraft.net or Launcher
Expected Outcome:
Successful login
Actual:
Failed to load https://authserver.mojang.com/authenticate: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://minecraft.net' is therefore not allowed access. The response had HTTP status code 403.
Replicated on firefox, Linux