Mozilla has Move this feature in recent updates from Network subpage on Settings/General to Privacy & Security with: Little to No warning or other notice No longer say what Encrypted DNS is used And while does save custom service like https://dns.quad9.net/dns-query Is Turned Off after this move to new setting page.
DNS over HTTPS and related is to stop ISP VPN and others sniffing DNS request.
I don't know or care about exact FF version. Most have auto updates and near no-one likely reads the update page even if that page has warning/notice.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
