monoPosixHelper error when receiving message with "permessage-deflate"

Contrary to Chrome, Firefox sends its websocket-client messages with the "permessage-deflate" extension, which causes a "monoPosixHelper" helper error in Unity upon reception of the first message. This error closes the connection to the client.

client code:
``
socket = new WebSocket("ws://192.168.20.223/get");

socket.onmessage=function(event){console.log("message:");console.log(event);}

socket.send("Hello World");
``

Use the supplied WebSocket client snippet to reproduce the failure in Unity, comparing Firefox's first message carrying the permessage-deflate extension with Chrome's behavior. Trace where that message is received and where the monoPosixHelper error closes the connection. Done means Firefox messages no longer trigger the error and the client connection remains open.