I mean, you could install a handful of them from the add-ons menu for the last few years, and depending on which fork you used, that list expanded quite a bit, and even included all* add-ons (though many are broken) via a list-system that basically forced the install of unsupported add-ons. But FF native is supposedly nearly ready to allow a slew of, in theory, tested and compatable add-ons, so this install-from-file feature is likely to test which work. I think I remember reading that a couple hundred add-ons are going to be enabled for mobile without trickery quite soon.