title: styling firefox extension button with background
body: <p>so I'm building a custom firefox extension and I got to the step where the toolbar is showing up and I put in buttons etc with css</p>
  
  <p>If you look at feedly's button (Feedly is a firefox extension), there is this nice rectangular background behind the button of the extension that makes it look like a legitimate clickable button: <a href="http://imageshack.us/photo/my-images/196/feedly.png/" rel="nofollow">http://imageshack.us/photo/my-images/196/feedly.png/</a></p>
  
  <p>whereas default extension buttons have no background behind it....</p>
  
  <p>how do you style a custom extension button such that it has a button-like background just like the feedly button? </p>