We don't support this yet (see bug 6003) and at least Webkit enforces this now. Seen on Safari on latest macOS.
Trying to open the HTML5 client in Safari on latest OS X gives the following error in the web console:
WebSocket connection to 'wss://eudemo.thinlinc.com:300/websocket/testuser/4' failed: Invalid HTTP version string: HTTP/1.0
Workaround in place until bug 6003 is fixed.
Tester should verify that the HTML5 client works on Safari 10 on OS X now.
Verified that commit solves the problem on safari 10.
(In reply to comment #0)
> We don't support this yet (see bug 6003) and at least Webkit enforces this now.
> Seen on Safari on latest macOS.
Firefox and Chrome works however.