It is bad form to block default UI,and it will only annoy and anger your users. The solution to this is to append your own menu to the default context menu. However, this cannot be done AFAIK. Probably a standard that allows that would be something worthy of consideration. So the only way to deal with this is custom UI elements. (As a Windows desktop developer moving to web development, I was quite dismayed that I couldn't simply get menu handle and append. In general, moving to straight jacketed webapps from desktop background where almost everything was possible was quite frustrating and painful.)