If you are going to use multiple browsers, then you might want to comment out the following line in the spider.php file:
PHP Code:
array_unshift($list_sites,$site_datas);
If you are going to use shell, then you might want to send in only one site per process.
Either way, you should test it out on some of your demo sites and see if it works, whether you need to do other modifications to the code, etcetera.