webrtc: not able to use signalling server from js

Trying to use the public signalling server https://webrtc.nirbheek.in/ and get "Too many connection attempts, aborting" error.

Here are the js logs:

Connecting to server wss://webrtc.nirbheek.in:8443 webrtc.js:57:13
Registering with server webrtc.js:57:13
Disconnected from server

So I tried running it locally as explained in the doc. It does work when using the session-client.py script but not when opening locally the webpage:

Connecting to server wss://127.0.0.1:8443 webrtc.js:57:13
Unable to connect to server, did you add an exception for the certificate?
Firefox can’t establish a connection to the server at wss://127.0.0.1:8443/. webrtc.js:236:14

I tried adding the generate cert.pem to Firefox's certificates settings but that didn't help. If an extra step is needed it would be nice to describe it in the doc as well.

cc @nirbheek