title: Sometimes Font Awesome only shows rectangle and numbers
body: <p>I'am using Font Awesone like this:</p>
  
  <pre><code>&lt;link href=".../css/font-awesome.min.css" rel="stylesheet" type="text/css"&gt;
  </code></pre>
  
  <p>and</p>
  
  <pre><code>&lt;span class="fa-stack fa-lg myownclass"&gt;
  </code></pre>
  
  <p>It works in IE, Chrome and Firefox - und sometimes in Opera. Now my customer told me, that he also not see the Icon on Firefox/Windows. </p>
  
  <p>Do you have an idea what's the problem? Opera sometimes shows me the Icons, sometimes only rectangles or numbers. </p>
  
  <p>Can you help me? Could it be a problem of caching?</p>