Only contact to firebog.net via DNS over HTTPS

[Bucking_Horn]

@Felixdk

When we now conclude that Pi-Hole cannot handle DoH requests and the browser is set up not to use DoH, it seems strange that DoH must be available to make contact.

I'd suspect that DoH isn't involved, but your DoH list is simply blocking an IP/domain that either shouldn't be blocked or cannot be blocked without also blocking wanted contents.

EDIT:
Searching for IPs has confirmed my suspicion:

$ dig +short firebog.net
185.199.108.153
185.199.109.153
185.199.110.153
185.199.111.153

Instead of allowing firewall clients to bypass your DoH rule, you could consider to either remove those IPs from the list, or explicitly allow them in your firewall.
/EDIT

You should consider to bring this to the attention of the DoH list's maintainer.