All of the machinery is in core, and will stay there (much of it is also depended on by the Tor uplift project's first party isolation features). This Test Pilot experiment is predominately about iterating on the UI.

Test Pilot isn't a "walled garden extension store." It's just a bunch of normal Firefox add-ons that are authored by Mozilla and happen to be explicitly experimental / ephemeral.

Yeah Test Pilot just is there to help us gather more data on how people use Containers so we can shape it's future. Lots of people are asking for features and we would like to concentrate on the ones that users would like.

Containers are indeed internal to the browser using origin attributes which are a platform feature. We have opened this up to extension authors also in WebExtensions so they can play with ideas also.

Thanks. Good to know containers are in the core.

Telemetry isn't an issue. If anything, it can be fully disabled. And yours is done right - all the data sent is properly described and observable. (Although it would be cool if there'd be a helper "let me decide later" mode when I can let browser collect data for a short while, get notified to review it, and then decide whenever it contains anything I consider sensitive or not...)

Maybe this is silly and irrational, but... While it's all your work (and thank you for this!) and decision, it just somehow doesn't feel right that an locally-installed software - no matter how experimental - is ephemeral, almost like it's not a software but a service. With normal AMO addons - even the experimental ones - I can browse the version history and roll back if something's not right. Test Pilot feels like end-user is completely out of control of whatever happens (unless they don't participate and just install from Git repos).

You're right. We keep control over the experiments so that we know the consistency of the data we're measuring.

A problem with using our full release channel Telemetry is that so many users have so many variables it's hard to compare apples to apples. E.g., was their performance issue caused by a setting, an add-on, the site they were on, or Firefox itself?

Test Pilot experiments give us some controls and parameters on the experience so we have a clearer idea of what's causing what.

The only main difference I can see besides the better UI/UX, is that you can create (and edit) containers, which you can't do in the Nightly version (or at least there is no UI for doing so). For instance you can create a 'Facebook' container, and then leave FB running in that, and not let FB track you across your life, cause that's just wrong. Before I kept FB in it's own Browser, which was annoying.

One surely can edit containers in Nightly. I did this for myself long time ago, when I've first learned about container tabs, as the default set was almost useless to me.

There's a setting, privacy.userContext.ui.enabled than enables management UI in the "privacy" section of "options" system (about:preferences#containers)

Awesome! I wasn't aware of this setting!