var old_height = 0;
function fixHeight() {
  new_height = $('main_content').getHeight();
  if( old_height != new_height ) {
    $('bottom_bar').setStyle({ height: new_height+'px' });
    $('bottom_fade').setStyle({ height: new_height+'px' });
    old_height = new_height;
    setTimeout("fixHeight();", 1000);
  }
}