You will know on forehand what the fixed DOH servers will be, how else would you be able to locate them?
If for example they will use the 1.1.1.1 DOH instance, you can simply redirect all localnet 1.1.1.1 (80/53) traffic to your own local (DOH)DNS(masq).
Besides that there must be a fallback option for network admins, since using dns filtering and localnet dns is very common in enterprise. Firefox implemented a canary domain, specifically designed for this purpose, see: https://support.mozilla.org/en-US/kb/canary-domain-use-appli...
If for example they will use the 1.1.1.1 DOH instance, you can simply redirect all localnet 1.1.1.1 (80/53) traffic to your own local (DOH)DNS(masq).
Besides that there must be a fallback option for network admins, since using dns filtering and localnet dns is very common in enterprise. Firefox implemented a canary domain, specifically designed for this purpose, see: https://support.mozilla.org/en-US/kb/canary-domain-use-appli...