[cremp]

They can, it just takes extra steps.

Firefox tries DoH via Cloudflare, for an internal domain that returns NXDOMAIN (Cloudflare can't answer for your internal resolver,) then they fall back to local resolvers, which is OS based (DHCP or statically set.)

The response time to complete the internal request goes up, because you're sending data to Cloudflare, they can't find it, then the 'normal' response time for internal resolvers.

Edit: Made more clear.

[ti_ranger]

> They can, it just takes extra steps.

For 99% of users, that means they can't.

Luckily for them, they probably aren't allowed to use Firefox anyway, and are stuck using Edge or whatever, and the local MCSE will use this as another reason why Firefox may not be used by anyone.