In this post, i will talk about configuring firefox browser to use DoH and not to fallback to OS native resolver Step 1 :- Configure DoH like the way it is mentioned here - https://support.mozilla.org/en-US/kb/firefox-dns-over-https . I am using https://doh.nkn.in/dns-query (which is the DoH server of https://www.nkn.in and in alpha testing stage) as my DoH server in firefox browser. Step 2 :- Check you configuration by typing about:networking#dns in the browser address bar. Most probably, you will see something like this -- Here, the DoH Mode option handles how firefox manages your DNS queries. This document (https://wiki.mozilla.org/Trusted_Recursive_Resolver) talks about the options available under 'DoH Mode'. So, if you want to use only DoH and not to fallback to native OS resolver, you can change the value of this parameter to '3'. Step 3 :- For changing the value of 'DoH Mode' parameter, type about:config in the browser's ...