(Original reply, heavily edited) My intention was to warn that Mozilla's use of the term 'Telemetry' as a feature does not cover all of their data collection,

(Original reply, heavily edited) My intention was to warn that Mozilla's use of the term 'Telemetry' as a feature does not cover all of their data collection, and to point to official examples demonstrating the mindset of the Mozilla developers for a higher-level perspective. As you have repeated, the one (primary) aspect of of Firefox's data collection that you mentioned (dubbed Telemetry, which I initially confused in context of OP's comment as intending to include all data collection) is documented on your link as opt-in. Props for that, but there are other aspects. (I am also going to verify it must indeed be enabled manually during a default install.) Per OP: The last thing I want is my browser to 'phone home' when it feels like it. I may be wrong, but my understading is that "Google Analytics in the add-on settings" has been improved only to _opt-out_ rather than being required in the past. Also, per their website SHIELD Studies seem to have a global opt-in followed by a per-study opt-in/out setting. Unfortunately the wording seems a bit wishy-washy and there are anecdotes on this discussion claiming this specific "study"/marketing opportunity did install and run something (at the very least: to skip enabling itself) without purposeful opt-in. There is a lot of confusion here. https://support.mozilla.org/en-US/kb/shield https://support.mozilla.org/en-US/kb/shield https://news.ycombinator.com/item?id=15956568 https://news.ycombinator.com/item?id=15956568 >Manishearth: What was enabled was a small piece of code[1] that would enable the full addon when a pref was flipped (Note: the Github link 404's since the add-on has been updated after this story broke.) https://news.ycombinator.com/item?id=15958466 https://news.ycombinator.com/item?id=15958466 >tosssh: Shield Studies are opt-out by default