doh-proxy works with doh-stub but not with firefox

[Chaz6]

I have set up an instance of doh-proxy at https://www.chaz6.com/dns-query (via an nginx proxy). I have verified it works with doh-stub, however when I set the following in Firefox (both latest stable and beta), dns resolution fails, and I am unsure what is wrong.

network.trr.uri = https://www.chaz6.com/dns-query
network.trr.mode = 3
network.trr.bootstrapAddress = 176.9.40.67

I would appreciate any help to find out what is broken.

[jedisct1]

I found the Firefox trr.mode=3 to be extremely unreliable. Once it starts working, it's fine, but at least on MacOS, it often just doesn't send anything at all.

Changing network.trr.bootstrapAddress to some random address back and forth seems to help start the process.

Also note that network.trr.bootstrapAddress has to be the IP address of a DoH server, this is not a bootstrap DNS server as in dnscrypt-proxy.

Which is why I'm wondering if the startup issue is not due to it requiring a valid certificate for https://<bootstrap ip>. That would explain why it seems to be more reliable with Cloudflare.