In the first place, if there is no centralized server, from which source will you get the list of your peers to connect to?
If your are planning for a private release of your software just between you and your friend you can still hard code both of your ip addresses to connect to each other or you will have no way to find each other.
But even so, if you know the ip address which you want to send a request to you will have to deal with the HTTP Security model on top of which WebSockets are based.
If the cross-domain network communications issues are not a problem for your specfic type of deployment (full public vs inside a business or private network), https://github.com/gimite/web-socket-js#readme may help you with their "HTML5 Web Socket implementation powered by Flash".
Chrome has also a way to let developers ask the user for network permissions by installing your web app as a Chrome app. But you are limited to the Chrome browser user.
Today you cannot host a MMO inside an HTML5 browser without a centralized server because of the security implications of the cross-domain HTTP policy restrictions.
If the choice of WebGL is not as much important for your project, you can be more easily accomodated with Unity with their full network stack.
Edited by MathieuDSTP, 17 February 2014 - 06:55 PM.