In the WebSocket spec, it only exists to open a connection to a url on a port, there is nothing about listening to a port for connections. You could open a connection to a server which can relay other websockets data, but you can't open a connection to another client. There is nothing in the spec to create a server basically.

That doesn't make any sense. The browser server just responds to websocket requests the same way a server would. The other browsers acting as clients wouldn't even need to know it was a browser just that it was acting as a websocket server.

With the current spec, how would you listen for connections?

The same way that websocket servers currently listen for connections. There are websocket servers in production and they have a standard way to listen for connections. All you would have to do is implement that same functionality.

I don't doubt you can implement that functionality, if you were the browser. But from the specs of Websocket currently in the browser, you cannot.