daveVk - 6:13 am on Mar 19, 2012 (gmt 0)

new Ajax.Request('g2.pl', options);

This results in the parameters being sent in the body of the post rather than as part of the url.

So either read the post body on the server or change to

new Ajax.Request('g2.pl?list='+encodeURIComponent(Sortable.serialize('firstlist')), options);