Firefox

It does not. ECH will work without DOH, but anybody listening can just see what site you’re querying from DNS instead of listening to SNI. Combining them is the most private.

Edit: This is wrong, in the sense that Mozilla has chosen to link the ECH setting with your DNS setting, even though they are separate. If you are using a local resolver, even if it is in turn using DoH or DNSCrypt upstream, Firefox won't use ECH and will instead leak SNI information to your ISP. This is disappointing behavior that from another company would seem designed to coax you into a certain direction.