the first ones were released with a physical switch behind the removable (shock horror) battery. Later ones have a magic key press that do the same thing (though one variant that Google sold directly had a flaw where the state was stored in volatile memory).

This is how people install things like Crouton and whole Linux distros.

Note btw that by default a Chromebook updates silently in the background (in a fashion that Android gained with 8.0).

It has two partitions, one is active one is dormant.

when a update is released, it gets applied to the dormant one. And on the next boot, the two a flipped. If the newly updated partition fails to boot, the system will switch them back on next reboot. And if it succeeds, it will become the active one while the older version goes dormant until another update is released.

Keep in mind that little if any state is stored locally.

And frankly, if Mozilla wants to get back in the game they should consider producing a similar system that also offer a set of backend services (or collaboration with others that can offers said services) and the means of bootstrapping such services independently.

Because right now while Chromebooks are being adopted rapidly in USA and Canada, European nations a weary thanks to the question of where the data is stored and who can potentially access them.