The linked paper to RAPPOR is really, really noteworthy here. In essence, Firefox will ask itself whether it visited website X and flip a coin and if it's head

The linked paper to RAPPOR is really, really noteworthy here. In essence, Firefox will ask itself whether it visited website X and flip a coin and if it's heads, it will lie to the server and send a random boolean. If it's tail, it will not. This way there is no way for anyone (including Mozilla) to know whether you actually visited the website. But the statistics will work out such that the collective data from everyone will give a good representation of all users. I find this a neat technology to collect data in a privacy-preserving way. And there's an opt-out (opt-in won't work because it creates bias and provides messy results). I really, honestly don't understand why people are so upset.