Firefox bypassing Pi-Hole even after setting Firefox network.trr.mode to "5"

[jfb]

@Gewehr98

I understand there is an upstream Canary resolver that Firefox is using, should I do something with that address?

No. This is already handled with Pi-hole, but it is only effective if the DoH setting in Firefox is enabled by default. If you have toggled it off and then back on, the canary domain will have no effect, since you have made a deliberate decision to use DoH.

https://github.com/pi-hole/pi-hole/pull/3166

Configure networks to disable DNS over HTTPS | Firefox Help

@Gewehr98

Firefox still pulls all sorts of ads that do not show up in the PiHole query logs

After you have eliminated DoH as a problem, ensure the host OS running on that client is using Pi-hole (and only Pi-hole for DNS):

Why should Pi-hole be my only DNS server?

Reduced Ad Blocking Capability The main reason you should Pi-hole as your only DNS server is that you will see increased performance in the blocking of ads. If you have two DNS servers (Pi-hole and something else), your network clients may not always query Pi-hole for name resolution. If a query happens to be answered from a non-Pi-hole DNS server, your block lists will not apply (since that DNS server doesn't know about them). All Queries Need To Go Through Pi-hole First Since other DNS serv…