title: Firefox computed margin auto returns 0
body: <p>I have a div which is centred horizontally with css :
      </p>
  
  <pre><code>.bar {
      height: 38px;
      width: 970px;
      margin-left: auto;
      margin-right: auto;
  }
  </code></pre>
  
  <p>I need to have another element to have same margin from the right as .bar, so I'm using <a href="http://www.bramstein.com/projects/jsizes/" rel="nofollow">jQuery sizes</a> for this :</p>
  
  <pre><code>&lt;div class="spec"&gt;I need to be aligned the same.&lt;/div&gt;
  </code></pre>
  
  <p>JS:</p>
  
  <pre><code>$(".spec").css('margin-right', $('.bar').margin().right + 'px');
  </code></pre>
  
  <p>This works, but not in Firefox 30.0, as it returns <strong>0</strong> for computed margin-right of .bar. Any suggestions ? <a href="http://jsbin.com/difobu/1/edit" rel="nofollow">http://jsbin.com/difobu/1/edit</a>.</p>
  
  <p><strong>$('.bar').css('margin-right') return 0px in FF 30.0 as well.</strong>
  If you donwnvote please provide an explanation.</p>