Remember browser doesn't know what is java and C#, it can only know what is javascript. So the event provide by browser is a javascript event. Whether an application running on browser supports mouse right click event or not is only according to if it present the event to developers.
When we want to handle right-click event, we must use System.Window.Browser.HtmlPage.Document.AttachEvent to attach the eventhandler for the javascript event oncontextmenu. And the limit that we have to set the windowless as false seems there is no way to avoid it.
Some people tell me that in MacOS, there is not the meaning of mouse right-click, I never use that. But both flash and silverlight don't support right-click defaultly, maybe this is the reason.
Regards!
Ling Bing
Bei Jing University of Aeronautics and Astronautics
Bei Jing, China