@firefoxwebdevs @alextecplayz No, everyone¹ has the same, simple definition of opt-in: the user must take some deliberate action in order to turn on the feature. It's really that simple.
You don't want to use the term "opt-in" because *you know it would be a lie*, as that page makes clear the user must take action to _avoid_ having the feature. That's called "opt-out".
1. OK, everyone who isn't being disingenuous slime. Like Mozilla, apparently.