The latest version of Firefox (96.0 and 95.02) has a bug when you enable DoH (DNS over HTTPS). It seems that it gets stuck at in the 'SocketThread'. In this post, i will show you how to fix your Firefox connection problems after enabling DoH.
To resolve this issues you can simply type 'about:config' in your Firefox url bar and disable the HTTP3 support by using the 'network.http.http3.enabled' keyword. Here you should change the value to false.
I hope this helps fixing your issue.