This overrides my DNS server, right? I use dnsmasq to rewrite all local addresses to their local IPs when I'm on my LAN, but it looks like this will break that.

One option is to use the .local TLD for local domains, those will never be resolved via DoH.rDoH. ref https://wiki.mozilla.org/Trusted_Recursive_Resolver

.local is reserved for multicast DNS so it is a really bad idea to use it for private DNS

Thanks for pointing that out, I'll stop recommending this.

Unfortunately that isn't ideal because the domains do resolve from the outside. I want my laptop to resolve to my router away from home, but to the actual computer inside the NAT when I'm home.

Maybe I just need IPv6.

Likely. Instead of using DNS at all, it performs its own HTTPS request to get the DNS results; maybe FF reads the hosts file first, though.

That's unfortunate, but I guess I can't have it both ways... It would be nice if this feature were disabled per-network, at least.