Example: The following HTML source code defines a section with a context menu. The menu has one item and a sub-menu with two items.

    <section id="noninteractive" contextmenu="imagemenu">
 
      <img src="html5.png" alt="HTML5" id="menudemo">
 
        <menu type="context" id="imagemenu">
          <menuitem label="rotate" onclick="rotate()"
                    icon="arrow_rotate_clockwise.png">
          </menuitem>
          <menu label="share">
            <menuitem label="twitter" onclick="alert('not yet')">
            </menuitem>
            <menuitem label="facebook" onclick="alert('not yet')">
            </menuitem>
          </menu>
        </menu>
    </section>

Naturally, you don’t need to rely on inline event handlers, all usual registration methods are available. When the context menu is activated, it looks like this:

The article also covers:

• How to check whether a browser supports context menus.
• How to dynamically enable/disable menu items depending on what state and app is currently in (active selection etc.): A menu fires a contextmenu event every time it opens.
• A CSS cursor called context-menu is available to give a visual clue as to where context menus are available.

You can try out context menus on a demo page.

Source: http://www.2ality.com/2011/11/ff8-html5-context-menus.html