title: Firefox Addon SDK: How to add Navigation Toolbar button and drop-down menu
body: <p>Developing a <code>Firefox Add-on</code>. Please someone help to add a drop-down menu with Navigation Toolbar button (like: <code>firebug</code>, <code>colorzilla</code>). I'm a newbie in this field.</p>
  
  <p>I've attached a screen-shot to show what I exactly want:</p>
  
  <p><img src="https://i.stack.imgur.com/ivMSO.png" alt="enter image description here"></p>