I tried a lot to get this in reality - using fedora silverblue. But that thing sucks. It is slow. Really dogslow. Devs are blaming rpm-ostree or btrfs - no idea. I wish there was something like ChromeOS but open.

Hint: Maybe firefox should pivot (re-do Firefox OS) to that.

It's pretty much rpm-ostree. Nobody bothered to make those workflows performant, so if you need to apply updates separately, it's going to suck. The OSTree download can be fast if you have a fast connection to the Fedora server, but it's not mirrored and there's no mirror network support (so no geographically close downloads). To be fair, bootc has this problem too because container tooling in general can't support mirror networks currently.