{
                $boxstring .= '<select name="' . POST_FORUM_URL . '" onchange="if(this.options[this.selectedIndex].value != -1){ forms[\'jumpbox\'].submit() }"></select>';
        }

Let the jumpbox work again in sites having additional session id checks.
   if ( !empty($SID) )
   {
      $boxstring .= '<input type="hidden" name="sid" value="' . $userdata['session_id'] . '" />';
   }

        $template->set_filenames(array(
                'jumpbox' => 'jumpbox.tpl')
        );
        $template->assign_vars(array(
                'L_GO' => $lang['Go'],
                'L_JUMP_TO' => $lang['Jump_to'],
                'L_SELECT_FORUM' => $lang['Select_forum'],

                'S_JUMPBOX_SELECT' => $boxstring,
                'S_JUMPBOX_ACTION' => append_sid($action))
        );
        $template->assign_var_from_handle('JUMPBOX', 'jumpbox');

        return;
}