public void AddMessageEventListener(string eventName, Action<string> action)
{
nsIDOMEventTarget target = Xpcom.QueryInterface<nsIDOMWindow>(WebBrowser.GetContentDOMWindowAttribute()).GetWindowRootAttribute();
target.AddEventListener(new nsAString(eventName), this, /*Review*/ true, true, /*what's this?*/2);
_messageEventListeners.Add(eventName, action);
}