I just noticed that my #Firefox was sending network traffic either with HTTP/2 + #ECH + #X25519MLKEM768, or with HTTP/3, but without ECH or X25519MLKEM768. Then I dug into about:config and found the option network.http.http3.enable_kyber, enabling it fixed the above behavior. HTTP/3 + ECH + X25519MLKEM768 is now used. Maybe check your Firefox behavior to ensure ECH and post-quantum key exchange is used whenever possible. Test site: https://cloudflare-ech.com/cdn-cgi/trace