title: Black box instead of iframe youtube video
body: <p>The code provided below is present in an html file.  When opening the file in Firefox there is a black box being shown instead of the video.  Does this mean an addon, extension, or application needs updating or a setting in Firefox needs changing?</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;body&gt;
  
  &lt;iframe width="420" height="345"
  src="http://www.youtube.com/embed/XGSy3_Czz8k"&gt;
  &lt;/iframe&gt;
  
  &lt;/body&gt;
  &lt;/html&gt; 
  </code></pre>