Can somebody point me to the place in the Firefox code where the "use-application-dns.net" canary domain is actually checked? I've tried searching the mozilla-c

Can somebody point me to the place in the Firefox code where the "use-application-dns.net" canary domain is actually checked? I've tried searching the mozilla-central Mercurial repository and I'm not finding it. I'm clearly inept here. I'm looking at what my Windows DNS servers return when I put in an empty zone for "use-application-dns.net" and I'd like to see exactly what Firefox is testing for. Windows 2012 R2, at least, returns the SOA and no NXDOMAIN for an "A" query to "use-application-dns.net" with an empty zone. If they're explicitly looking for NXDOMAIN then blocking DOH behavior with Windows DNS servers probably isn't going to work. >sigh<