title: contentWindow.document.execCommand('print', false, null) not working in firefox
body: <p>I am implementing some print function for iframe now , and i am using below code:</p>
  
  <pre><code> $('#printBtn').click(function(){
       var iframe = document.getElementById('previewInfoBodyFrame');
       iframe.contentWindow.document.execCommand('print', false, null);
       return false;     
  }); 
  </code></pre>
  
  <p>but i found that in firefox browser, it's not working , but for IE,chrome and safari, it works fine. searched a lot but cannot figure out how this happening. anyone can give some ideas? Thanks</p>