So, das sollte auch unter Linux funktionieren:

Components.utils.import("resource://gre/modules/Microformats.js");

jetpack.statusBar.append({
  html: '<img src="http://microformats.org/favicon.ico">
           hCards: <span id="hcard-count">0</span>',
  onReady: function(jetpackWidget) {
    function counthCard(){
      //load HTML
      var doc = jetpack.tabs.focused.contentDocument;
      // count microformats
      var uFcount = Microformats.count('hCard', doc);
      if (uFcount > 0) {
       $(jetpackWidget).find('#hcard-count').html(uFcount);
      }
    }
    jetpack.tabs.onFocus(counthCard);
  }
});