For an article supposedly about protecting your privacy, it's very weird to see the author's opposition to DoH. The only evidence given are the "Criticism" section of the wiki article on DoH (which no longer exists, apparently), some blog post and a Reddit comment with few convincing arguments (no, pointing fingers at SNI and the like isn't gonna cut it).
DoH has issues but is overall a net positive and step in the right direction, and you have the freedom to set the DoH server to whichever you think is less evil, but to go as far as to block it is just strange.
I agree DoH has strong benefits. However, should your web browser (or any specific app for that matter) have its own resolution settings? What about split-horizon DNS on your LAN? What about cache/latency when your uplink to CloudFlare is really bad (as in many so-called developing countries)?
I'd be much less concerned if Firefox gave users an explicit choice about this: "Your Internet provider may be censoring/monitoring domain names. Would you like to keep it, or use a slower secure tunnel to one organization in the list below? Note that local-network services may break due to using an alternative."
Defaulting to CloudFlare is a joke. Just like telemetry has not helped Firefox improve in significant ways from my perspective as a user. Just like using Google Analytics on Mozilla websites was always hypocritical. Just like integrating more cloud services (Pocket, Sync, VPN) into Firefox without worrying about how to make it practical to selfhost is helping the web move in a bad direction.
I have much respect for Mozilla devs, but being run by corporate executives not the community has definitely killed Mozilla's mission. I'd be much more inclined nowadays to trust a non-profit where each employee has equal pay, team management is done or elected by the team and overall governance is left to the community. I just don't know of any browser vendor that suits the bill.
DoH has issues but is overall a net positive and step in the right direction, and you have the freedom to set the DoH server to whichever you think is less evil, but to go as far as to block it is just strange.