Firefox can't establish a websocket connection while Chrome can

I'm developing a webapp and I'm including websocket connectivity. I've installed a websocket server with node.js (5.0.0) with websocket (https://www.npmjs.com/package/websocket).

In Chrome it works perfectly but in Firefox this message appears in console:

Firefox no puede establecer una conexión con el servidor en wss://www.my-dev-server.com:1337/.

(Firefox can't establish a connection with server at...)

This is the server code (basically as in examples):

var WebSocketServer = require('websocket').server;

var https = require('https');
var fs = require('fs');

var options = {
  key: fs.readFileSync('/keyfile.key'),
  cert: fs.readFileSync('/pemfile.pem')
};
var port = 1337; 

// Create HTTPS service.
var server = https.createServer(options, function(request, response) {
    console.log((new Date()) + ' Received request for ' + request.url);
    response.writeHead(404);
    response.end();
});     

server.listen(port, function() {
    console.log((new Date()) + ' Server is listening on port ' + port);
});

// create the server
wsServer = new WebSocketServer({
    httpServer: server,
    autoAcceptConnections: false
});

function originIsAllowed( origin ) {
    // TODO: complete
    return true;
}

var clients = [];

// WebSocket server
wsServer.on('request', function(request) {

    if( !originIsAllowed( request.origin ) ) {
        request.reject();
        console.log((new Date()) + ' Connection from origin ' + request.origin + 'rejected.');
        return;
    }
    console.log((new Date()) + ' Connection accepted from ' + request.origin + '.');

    var connection = request.accept(null, request.origin);
    clients.push(connection);

    connection.on('message', function( message ) {
        if (message.type === 'utf8') {
            console.log('Received Message: ' + message.utf8Data);
        }
        else if( message.type === 'binary' ) {

        }
    });

    connection.on( 'error', function( error ) {
    });

    connection.on('close', function( reasonCode, description ) {
        console.log((new Date()) + " Peer " + connection.remoteAddress + " disconnected.");
    });
});

I use a self-signed certificate for development purposes, the same that is used by the web server.

This is my client code:

var connection = new WebSocket('wss://www.my-dev-server.com:1337');

connection.onopen = function () { };

connection.onerror = function (error) { };

connection.onmessage = function (message) {
    /* some code here */
};

I, finally, found a solution.

The problem was that for https connections, in port 443, Firefox had already stored an exception for unknown certificate while it needed another exception for wss (port 1337 in this case).

I've added a certificate exception, in advanced preferences, for this port and now works fine.