Is it possible for two different web pages to use the same cookie? For example, some news sites now have buttons on the bottom, where if you are logged into facebook, you can just click the button to "like" the article. Is this a case of a 3rd party website using facebook's cookie to know which account you are, and if so, is there a way I can control it?

I'm not sure how the new "like" system works, so maybe the button part isn't actually on the news site, but hosted on facebooks servers or something, so it's really facebook itself accessing its own cookie. If that's the case, is there a way I can choose when a site accesses its own cookie?

Thanks for any help!