title: Javascript workaround for firefox iframe getComputedStyle bug
body: <p>I'm trying to use the following workaround for the hidden iframe/getComputedSytle firefox bug <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=548397" rel="nofollow">548397</a>.</p>
  
  <pre><code>if (/firefox/i.test(navigator.userAgent)){
     window.oldGetComputedStyle = window.getComputedStyle;
     window.getComputedStyle = function (element, pseudoElt) {
        var t = window.oldGetComputedStyle(element, pseudoElt);
        if (t === null) {
           return {};
        } else{
           return t;
        }
     };
  }
  </code></pre>
  
  <p>However in my case I also need <code>getComputedSytle.getPropertyValue</code>  i.e. I get the following error:</p>
  
  <pre><code>TypeError: my_window.getComputedStyle(...).getPropertyValue is not a function
  </code></pre>
  
  <p>How can I add <code>getPropertyValue</code> to the above workaround?</p>