NextDNS purports to be a DNS provider that will use public blocklists and filter queries and block ads and tracking like a PiHole.
The Mozilla TRR policy states that the DNS provider must not filter any queries unless the user explicitly opts-in.
How would a user selecting NextDNS as a TRR indicate that she wants NextDNS to filter queries in order to block ads and tracking.
The TRR policy also states that the provider must not use the EDNS Client Subnet extension. It looks like NextDNS does use some modified version of ECS, at least in its plaintext DNS service.
The FAQ states users can submit a query with class CHAOS instead of IN to get some diagnostics, e.g.,
drill -t example.com @45.90.28.0 a chaos
Unfortunately, someone who ISP is filtering port 53 cannot make this query.
