World's Simplest Privacy Tool
Here's the world's simplest Firefox add-on, which just turns on Tracking Protection (ordinarily buried somewhere in about:config) and sets third-party cookie policy to a sane value.
install pq from addons.mozilla.org
So far it has 15 users and one review -- five stars. It doesn't do much, or for very many people, but what it does do it does with five-star quality.
Bonus link: How do I turn on Tracking Protection? Let me count the ways.