I can also confirm that something goes haywire when you enable the Cloudflare DoH option in FF 87.
Both of the following pages give random YES and NO results for DoH and Secure DNS test results
✌️✌️ Browse a faster, more private internet.
1.1.1.1
Secure DNS Transport using DoH (DNS over HTTPS) or DoT (DNS over TLS) and SNI with ECH
www.cloudflare.com
I tested this issue by using DNSCrypt and enabling Cloudflare resolvers only . Now it always gives the exact same result
on both pages. The Enable DNS over HTTPS option has to remain unticked in order for DNSCrypt settings to work correctly.
The advantage of using DNSCrypt is that your entire system including the FF browser is setup to use DNS over HTTPS.
I am sure the same result can be achieved with YogaDNS.
So it does look like there is indeed an issue with the current Clouflare DoH setting in FF 87.