I'm not sure there's much of a difference in practice? Firefox is implementing the Firefox-specific V3 webextension API (at least, most of it) that they have o

I'm not sure there's much of a difference in practice? Firefox is implementing the Firefox-specific V3 webextension API (at least, most of it) that they have on Desktop, and they're also turning on support for installing addons from the AMO generally rather than just a subset of curated addons. So it's sort of both (with some emphasis on "turning on" because as far as I know a decent portion of the API was already implemented before this point).