Well, yeah. This was one of the significant reasons against Cloudflare's DoH too. They want all Firefox users to use their DNS resolver and deprive the ability of competing DNS-based CDNs (most CDNs) to pick good nodes in Firefox. I've been thinking of blacklisting Cloudflare completely on all of my servers just for that. And it seems Firefox will even be able to detect that and fallback to proper DNS for such domains.