title: Facebook conversion tracking pixel seems to be fired double
body: <p>i'm using the Facebook Pixel tracking in one of my (shopping) sites i'm supervising.
  For this, i put the standard code into the head section or better said into the head.phtml for a more generic way of handling.</p>
  
  <p>The PageView pixel is fine all the time. But on my checkout success page there is some strange behaviour, because Facebook Pixelhelper tells me first, that the Pageview is loaded successfully. After that, it tells me that the Purchase Pixel is also loaded successfully. And as last, it tells me that the Purchase Pixel did not load. In the FB Pixelhelper the 1st and 2nd pixels are shown fast (Pageview and Purchase), then it takes ~1-2 seconds until the 3rd pixel appears in the list.</p>
  
  <p>The 1st purchase pixel in the FB Pixelhelper shows the URL called for the purchase and all is fine. The 2nd purchase pixel just shows the fbq - track like shown later.</p>
  
  <p>I've included the track in a script tag on the onepage checkout success page with the code:</p>
  
  <pre><code>fbq('track', 'Purchase', {value: '&lt;?php echo number_format($total, 2, '.', ','); ?&gt;', currency: 'EUR'});
  </code></pre>
  
  <p>There is no other occurency of any Purchase track in the HTML code.</p>
  
  <p>As i do not have access to the FB Backend for tracking, i can't do any checks against code changes.</p>
  
  <p>Even more interesting: On the development system all is fine. The only difference is no https on the checkout. The fbevents.js is included like intended to be with <code>//connect.facebook.net/en_US/fbevents.js</code> so i think, this shouldn't be the problem at all.</p>
  
  <p>Any ideas how i can track this double firing or fix it? Or is there a known issue?</p>