Splendid Rated 5 out of 5 stars
this feature should be permanently included in the upcoming Firefox 3 release.
to the author .. please keep updating it i've been using it since it first got out and there's no other better cookie manager than this one.
this extension will let you keep(protect) the cookie you want and delete the rest every time firefox starts (optional).
this is a very useful and must have utility for privacy conscious people out there.