Differential privacy does statistically disclose information about you, and whether the quantitative bound used is up to your standards is a decision you should make before it happens. Given that user-level understanding of DP is so low, I don't think defaulting people in to levels chosen by others is a good idea. I 100% guarantee Mozilla doesn't have the background to make this choice responsibly, and doesn't have near the DP expertise the RAPPOR team has / had (who I also wouldn't trust to chose things for me).

Ideally, the use of differential privacy would make you more willing to opt in (when you have a choice) rather than being a smokescreen for organizations that simply want to harvest more data (which was Mozilla's stated motivation).

Edit: fwiw, there are some cool "recent" versions of differential privacy that let the users control the amount of privacy loss on a user-by-user basis. So, you could start at 0 and dial it up as you feel more comfortable with the tech. This incentivizes organizations to be more transparent with what they do, as it (in principle) increases turnout.

Edit2: For context, Apple's "default" values appear to be (from this paper) epsilon = 16 * days. That means that each day you are active, the posterior probability someone has about any fact about you can increase by a factor of exp(16) ~= 88 million. So, numbers matter and I am (i) glad Apple made it opt-in, (ii) super disappointed they aren't at all transparent about how it works, and (iii) thankful that the paper authors are doing this work.