Firefox admits they will eventually be sending all of your DNS to Cloudflare. Cloudflare will monetize your internet browsing, no matter how much their PR people say they are.
If you want to disable that, go to "about:config", and set "network.trr.mode" to 5.
The values are: 0 - default off, 1 - race, 2 TRR first, 3 TRR only, 4 shadow, 5 off by choice