Android: Part of the problem with Facebook privacy is that you can still be tracked even when you're not on Facebook itself. Tinfoil for Facebook helps prevent this by browsing the mobile Facebook site in a sandbox.
The way it works is that the app loads Facebook's existing mobile site (which we like) in a wrapper. As long as you're also logged out in Chrome or your browser of choice, Facebook can't track any of your other browsing habits.
Some users have reported that certain features don't work, which is to be expected -- the app itself isn't intended to be anything more than a wrapper for the mobile site. However, it could be worth it for the piece of mind.