about:config -> search for network.trr -> set network.trr.mode = 5 to completely disable it (I do not recommend this)
The curl wiki has a list of DOH servers: https://github.com/curl/curl/wiki/DNS-over-HTTPS
It should also point to "the other side of the story", the benefits of DOH over classic DNS resolving, for example https://hacks.mozilla.org/2018/05/a-cartoon-intro-to-dns-ove...
For example, when the user roams among several networks, and each of them has split-horizon DNS, the user is not going to re-set their setting after connecting to each specific network. Throw in VPN connections and their DNS settings, and you have quite a problem at hand.
There's a reason why DNS settings are traditionally set system-wide via DHCP, not statically. This is a step backwards.
Mozilla has stated plans to eventually turn it on by default[2] but I have yet to see any timeline or details of what the default config will actually be. Your article seems to assert that it will be on by default in FF62, where did Mozilla ever say this? Everything I have read seems to indicate that FF62 is just adding support, which is off by default, and requires a change to about:config to enable in the first place.
[1] https://gist.github.com/bagder/5e29101079e9ac78920ba2fc718ac...
[2] https://blog.nightly.mozilla.org/2018/06/01/improving-dns-pr...
While CloudFlare is being used for the opt-in study, you have no evidence that they will be used in any on-by-default scenario. Nor do you have any evidence that only a single DoH provider will be used globally.
Perhaps you should monitor Mozilla mailing lists.