Thx! And seems that `use-application-dns.net` works for me. But I will still consider replacing Firefox, because this behavior, which is inconsistent with the settings, is unacceptable to me. However, I'm glad I learned a new thing, thx again :)
Suggested capture methods:
tcpdump -p --dont-verify-checksums -i any -NNnntt -B32768 -c2000 -s0 proto 6 and 'tcp[13] == 2' and not host ${Your_Router_IP} &
tcpdump -p --dont-verify-checksums -i any -NNnntt -B32768 -c4000 -s0 proto 17 and not host ${Your_Router_IP} and 'length <256' &
Don't paste the output, just suggestions for capturing HTTPS SYN and QUIC over UDP.