Re: Mozilla
it's not been enabled by default for UK to avoid clashing with censorship in this country.
It's not been enabled by default anywhere yet because it's still a slightly experimental implementation and they've been working out the bugs with (for instance) detecting captive portals and ensuring people in enterprise environments are able to reliably manage/override it in Group Policy, etc. No bloody good enabling it by default and making the internal infrastructure of enterprises, hospitals and other big networks inaccessible because the browser has decided to phone it's own DNS out to Cloudflare.
It's there for the tyre-kickers on the nightly builds to report issues.
That said, you are correct that when/if it does become "by default" Mozilla have said that won't include the UK. We'll have to turn it on manually if we actually want it (which quite a lot of people won't because they want their System/OS resolver to connect to their internal DNS/Active Directory/PiHole which will then use DNS-over-TLS or -HTTPS to do external resolution).
Biting the hand that feeds IT
