Privacy Badger 1.0 has been released some time ago. If I could install a single Firefox extension only, it would be this one. It’s very easy to use, effective (AFAICT) and doesn’t cause problems; much better than the other privacy extensions I used (although they can still be useful for special purposes). I can recommended using it, as well as reading the FAQ and supporting the Electronic Frontier Foundation (EFF). BTW, another very useful web browser extension by EFF is HTTPS Everywhere. Good work, EFF! Looking forward an Android version as there is currently very little one can do to protect his privacy in Firefox for Android.