Firefox can’t establish a connection to the server at wss://

Question

I have installed Ratchet websocket through for my website that is under https:

php ~/composer.phar require cboden/ratchet

then I have set the bin/server.php:

[...] class Chat
$server = IoServer::factory(
    new HttpServer(
        new WsServer(
            new Chat()
        )
    ),
    8888
);

$server->run();

then I have enabled mod_proxy.so and mod_proxy_wstunnel.so:

root@ubuntu:~# a2enmod proxy_http 
root@ubuntu:~# sudo a2enmod proxy_wstunnel 
root@ubuntu:~# sudo service apache2 restart

After that I changed the file /etc/apache2/sites-available/000-default-le-ssl.conf and added this line:

<IfModule mod_ssl.c>
<VirtualHost *:443>
        ProxyPass /wss2/ ws://mywebsite.org:8888/
        ...

And runned this:

sudo a2ensite default-ssl.conf
sudo service apache2 restart

After that I started the server:

php bin/server.php

And now I connected in the webpage that has this socket connection:

const ws = new WebSocket('wss://mywebsite.org/wss2/?1b70ee9e56888665cfbde77ec832de8a');

But I obtain the title error. In localhost environment I don't have any error and the app works