I think it's kind of strange that they are planning to enable DOH by default;

Your ISP can see all connections/ip addresses you connect to regardless of whether you use your ISP's DNS servers or not. So, in the end by using DOH in Firefox (= Cloudflare's DNS by default) you're just sharing your internet history with yet another third party.

This may be beneficial for some people where ISP's mess with DNS resolving, but for many other people it's actually a regression in privacy (especially if you live in a country that has higher privacy standards/laws than the US.)