Ullebe1

Ordinary DNS requests are always plaintext and readable to anyone between you and the DNS server. So regardless of which DNS server you use, your ISP can see all your DNS lookups. For any amount of privacy for DNS, the minimum is something like DNS-over-TLS or DNS-over-HTTPS, the latter of which Firefox uses by default in some countries and supports everywhere.

True. Luckily it seems Mozilla has been preparing for this in advance: https://www.macrumors.com/2023/02/07/mozilla-developing-non-webkit-version-of-firefox/

Luckily this will change next year with the new EU rules, as they explicitly call out allowing alternative browser engines.