I thought Mozilla was the one behind ECH. How is it enabled in Chrome, Edge, and Opera and not in Librewolf, let alone Firefox?
Is this a false negative from https://privacytests.org?
What is ECH and GPC?
ECH: Encrypted Client Hello
GPC: Global Privacy Control
I don’t really understand these specs on a deep level, so I can’t summarize them for you, but these articles should be able to answer any questions you have: