I'm not talking about Pocket.

I'm talking about A/B testing internal features exactly like Chrome, such as ip v4/v6 path preference, pipelining support, TLS faststart (and so on) according to a random cohort selection.

While you can certainly turn off these sorts of features, I just want to emphasize that these are intended to make the product better, and Mozilla abides by a fairly strict privacy policy (when comparing to most tech companies at least):

https://www.mozilla.org/en-US/privacy/firefox/

The intention is to ship features that people actually want, and to ensure that Firefox is actually working for people (not everyone can/will file bug reports or post on twitter or hackernews etc)

Exactly like Chrome. I do not argue about the good intention behind.