Debugging JavaScript cookies can be an absolute nightmare, but the FireCookie extension makes it easy by allowing you to inspect and edit cookies, including permissions, expiration time, and values. You can use it to sort cookies by domain and disable global or local cookies.
It seems that whatever the development task, there's a Firebug extension tool to address it, and every one is open source and freely available for download. It's hard to imagine a more useful and comprehensive set of tools for any web developer.