After much time I found that the latest Firefox update does allow quad9 DNS resolution only as a administrator account, on both my Windows 10 pro and Windows 11 pro lap-tops, However when I login either as a “user” (non admin) it refuses and only uses Cloudflare! I did as you suggested as well as removed Cloudflare from the Windows registry using the registry editor. This just began since the latest Firefox update last week. I have 2 lap tops, and on both have 3 browsers. This occurs on either version of windows only when logged in as non administrator. I hope you will report this to Mozilla to fix this discrepancy as quad9 is also a great DNS resolution solution and is faster from my location. I have been using quad9 for the last 2 years and never had this issue until latest Firefox release! Edge and Brave browsers are not any issue. Firefox is able to bypass both my router and windows pro settings whenever non admin login is used! I set to use DoH "Non Proxy" and it did not work either, nor removing Cloudflare from registry. I set my my router and Windows both to use QUAD9. How Firefox can bypass my configs (ip4 and ip6) when logged in as a standard user is beyond my level of expertise. Someone please report this bug. Much THANKS Happy Holidays to all. Firefox was always my preferred browser until last week.