WebSockets not working, use of Google Firebase causes render crash

[Stesteste]

I am trying to connect to Google Firebase from a page I show in a QWebEngineView and the moment the following line is executed, the render process crashes (i.e. renderProcessTerminated is signalled).

var ref = new Firebase("https://my-project.firebaseio.com/");

Also, I cannot establish a WebSocket connection. I get an error that it failed for an unknown reason.

Could these two be connected? I built the webengine from source here. Many things are working alright, e.g. YouTube.

[Stesteste]

The exit code of the renderer is 3.

[Stesteste]

Ok, it seems that WebSockets don't work fore me. If I force Firebase to use long-polling via

Firebase.INTERNAL.forceLongPolling();

before creating the Firebase object, then it works.

I have webengine 5.9.1 built against qt 5.6.2. Has anyone tried websockets in this constellation?