Calling scroll.next() seems to take longer to return results after a few calls to it

[magician11]

Here is an example how I am using this library

  var profilesToLoadAtATime = 18;
  var numberLoaded = 0;
  var loadingMore = false;
  var startTime = Math.floor(Date.now() / 1000);

  // lazy load teachers by last name
  var scrollRef = new Firebase.util.Scroll(ref, 'lastName');
  scrollRef.on('child_added', function(snap) {
    appendTeacher(snap);
    numberLoaded += 1;

    if(numberLoaded % profilesToLoadAtATime === 0) {
      $('.search-info').hide();
      loadingMore = false;
      console.log('Time taken = ' + (Math.floor(Date.now() / 1000) - startTime));
    }
  });
  scrollRef.scroll.next(profilesToLoadAtATime);

  $(window).scroll(function() {
    if($(window).scrollTop() + $(window).height() > $(document).height() - 800) {
      if(!loadingMore) {
        console.log('loading more profiles...');
        startTime = Math.floor(Date.now() / 1000);
        loadingMore = true;
        scrollRef.scroll.next(profilesToLoadAtATime);
        $('.search-info').show();
      }
    }
  });

Basically the first load is quick.. 2 seconds. Then calling scroll.next() again.. quick 3 seconds.. then the load times start to jump right up.

Sample output...

loading more profiles... Time taken = 2 loading more profiles... Time taken = 3 loading more profiles... Time taken = 6 loading more profiles... Time taken = 23 loading more profiles... Time taken = 13 loading more profiles... Time taken = 17 loading more profiles... Time taken = 17 loading more profiles... Time taken = 15 loading more profiles... Time taken = 17 loading more profiles... Time taken = 22 loading more profiles... Time taken = 24 loading more profiles... Time taken = 36 loading more profiles... Time taken = 21

Any idea why? Am I missing something? Thanks.