Exactly - sometimes I'm happy for sites to know who am I, what toothpaste I like, etc, or for them to try to sell me stuff I might like. However, what I don't

Exactly - sometimes I'm happy for sites to know who am I, what toothpaste I like, etc, or for them to try to sell me stuff I might like. However, what I don't want is a tracking beacon, where one provider (Facebook spring to mind) track all my activity on the web, and provide slices of that to other sites.