Mozilla's new DNS is a MITM attack disguised as a security upgrade.

"What Mozilla effectively does is adding a SPOF for all of their users. But the main problem is not that if cloudflare is down that nobody can surf anymore. No, the real problem is that it fully disables anonymity. Think about a whistleblowler who wants to send information to a newspaper. In the days before Mozilla's change, the DNS resolution was local and could be attacked. However with Mozilla's change, all DNS requests are seen by Cloudflare and in turn also by any government agency that has legal right to request data from Cloudflare.

Let's stop here for the moment and repeat: With Mozilla's change, any (US) government agency can basically trace you down."

https://blog.ungleich.ch/en-us/cms/blog/2018/08/04/mozillas-new-dns-resolution-is-dangerous/

This is assuredly by design.  Mozilla is not your friend.