I do not want a centralized service that my browser connects to for
any reason, and HTTP3 sounds like a lot of trouble for very little gain.
You argue that it wasn't an automatic update: I am pretty sure that the first install on this machine did not have HTTP3 support and that automatic updates pulled it in, end of story right there.
As for the telemetry issue: that's even worse because telemetry and all other forms of communication with the mothership other than automatic updates have been disabled on this machine, and has been silently re-enabled without my consent. That's a pretty gross violation of trust, and if that in turn causes me to lose a morning then that makes it even worse. Fortunately, today is not an interview day, but if this had happened two days ago the consequences would be terrible.
Finally, automatic updates would ideally just fix security issues and not introduce new, possibly unwanted functionality. I carefully select my tools for their purpose and I absolutely hate this brave new world where critical stuff suddenly stops working because some company could not be bothered to take their end users' interests a bit more serious.
Google and Cloudflare were not implicated here, it was FireFox that stopped working, Chrome still functioned just fine.