Adding objects to ListModelList causes Firefox to complain slow script

From version 5.0.8, when i try to add some items to the model of a listbox (ListModelList) through the method ListModelList.addAll(int index, java.util.Collection c), the rendering of new items (100 items added each time) has become very slow compared to version 5.0.7.1 (about the double of time), and I get an error message on Firefox, complaining a slow script on:
.../zkau/web/72bddcc9/js/zk.wpd:13