Eumm... I am about to go to bed, so tired, and I did not check your
email in depth, but I have an idea. Firefox has its own DNS service,
doesn't use the system service, so you can get weird results.
Look for "DNS over https" in settings, I think that is the name. Unset
that, and try again, maybe it helps, or at least, gets you consistent
results with other browsers.
DNS over HTTPS is disabled in Firefox (it was already, did not change it).
Unfortunately, I have three different behaviors: Firefox, Falkon, the rest of the world (curl, wget, Chromium), so having consistent behavior is tougher than it might seem :-(
Cris