Access within PC's firefox only allows deleting cookies (all / individually). So it is possible to solve particular problem. For instance, if you have problem with facebook site, search for facebook cookies and delete them all (Tools-Options-Privacy-remove individual cookies), then visit again facebook site and login with checked box for permanent logging.

Maybe there are other ways to manage stored logging policy inside cookies.sqilte file with some tool, but I'm not familiar with it. Try to search on Google, maybe you will find something useful.