Is Opa using AJAX or Websockets? I guess this will be the first. What if I want to use websockets instead of AJAX? Or it looks like socket.io for Javascript - if the browser supports the Websockets it uses, otherwise it returns to AJAX and Flash sockets.
OPA does not currently support websockets.
But this is something we will look at again, since firefox 6 brings back support for web maps, and a fix is proposed for the previous big security issue.
Opa currently uses AJAX.
Also, I think the website is rarely supported (by browsers) at the moment due to security concerns. And the RFC is still in the project.
Opa servers do not currently support websocket.