In fact, Firefox has increased in the amount of unwarranted telemetry and "experiments" a lot in the last years, a direction I'm really not happy with.
The main difference is that Firefox still gives you pretty liberal access to most internal settings, while Chromium is abysmal, if not ridiculous.
I can understand "experiments" (Pocket comes to mind), but what are you referring to wrt "unwarranted telemetry"?
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.
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)