title: Close Firefox download file popup from extension
body: <p>I have a Firefox extension. The extension opens a tab and loads some URL.<br>
  If it links to a file with specific MIME type (zip, flv) the the FF opens a download dialog.
  How can I close this window?
  If I use <code>gBrowser.addProgressListener(nsIWebProgressListener)</code> I can stop loading page but I can't close a window. 
  I try to use <code>nsIURIContentListener</code> interface, but this interface works only when MIME type is not standart, when it is <strong>text/html</strong> it doesn't work.</p>
  
  <p>relevant link: <a href="http://forums.mozillazine.org/viewtopic.php?t=501254&amp;sid=a2f27a7ca70ecb78ef834d80ec86286e" rel="nofollow">Intercepting URL in Firefox extension</a></p>