Firefox enables this feature by "default" which cripples any DNS filtering you've done on your own networking setup.
To disable the DNS-over-https feature:
about:config
in the browser's address barnetwork.trr.mode
and set to 5, to disable it completelydoh-rollout.previous.trr.mode
to 5Setting to 0 instead of 5 should have the same effect. 5 signifies it was user-disabled and 0 indicates off/automatic.