Everything here applies to Firefox version 119. It is not available in Firefox 115.4 ESR.
Encrypted Client Hello (ECH) is now available to Firefox users, delivering a more private browsing experience. ECH extends the encryption used in TLS connections to cover more of the handshake and better protect sensitive fields. Read more about the launch of ECH on Mozilla Distilled. For further details on how ECH interacts with Enterprise policies, TLS middleboxes and other technology, see our FAQ and MozillaWiki for experts. This is only available in Firefox 119.
