title: Mailto-link as menu-item in toolbarbutton-menu possible?
body: <p>I'm using Erik Vold's toolbarbutton API with Mozilla's Addon-SDK and was wondering if there is a way linking a menu-item in order to open a mail programm onclick.<br>
  For a widget this is trivial since I can just add a <code>&lt;a href="mailto:xxxxx"&gt;&lt;/a&gt;</code> to the HTML of the corresponding panel.<br>
  But what about the toolbarbutton-menu? Is there anything like <code>type: "email"</code> for instance which would allow modifying the toolbarbutton API?    </p>
  
  <p>EDIT:<br>
  What I already tried without success:<br>
  giving the menu-item href attribute (including class <code>text-link</code>)<br>
  adding anchor element as childNode to menu-item</p>