Ajax.Responders.register({
  onCreate: function() {
    Ajax.activeRequestCount++;
    if (!$('ajax_indicator').visible()){
      $('ajax_indicator').show();
    }
  },
  onComplete: function() {
    Ajax.activeRequestCount--;
    if (Ajax.activeRequestCount == 0){
      $('ajax_indicator').hide();
    }
  }
});