Why is this javascript getting permission denied?
<blockquote>
<pre><code>Permission denied for &lt;http://example.com&gt; to get property
</code></pre>
  
  <p>HTMLDocument.body from
  <a href="http://www.example.com" rel="nofollow">http://www.example.com</a>.</p>
</blockquote>

<pre><code>var c = parseFloat(cf.contentDocument.body.offsetHeight) + 30; 
</code></pre>
