HTML5 context menus in the wild: Twitter’s “Follow” button
Twitter’s “Follow” button has an HTML5 context menu . The button below allows you to try it out. On Firefox, you get a context menu whose top three items are “Follow”, “@rauschma on Twitter” and “Tweet to @rauschma”. Alas, other browsers don’t support the customization of context menus, yet. jQuery contextMenu is a polyfill  that works on all browsers and uses HTML5 on Firefox. There are plans to parse HTML5, but they are waiting for a second HTML5 implementation before they do that.