Re: So its all as clear as mud!
It would seem that in getting DoH "out there", Mozilla have stepped over a boundary with their client implementation; a boundary it would seem Google and MS are being a little more respectful of.
I anticipate that once MS deliver a W10 build with DoH support, Mozilla will fall back into line.
However, this just leaves a small problem, MS are only implementing DoH in a future W10 build (but still no word on W10 DNSsec) - increasing the impetus to migrate away from W7 et al, so surviving W7 & 8 systems may benefit from a current Firefox style client that avoids the host systems DNS resolver. Additionally, it is not clear which versions of Windows server will get support for DoH.
Aside: interesting article here from MS: Windows will improve user privacy with DNS over HTTPS - key quote "we are making plans to adopt DNS over HTTPS (or DoH) in the Windows DNS client.", so may arrive in a couple of years.