My understanding is that the FF softtoken was intended to be temporary while they worked on their HID support. That might not be the case any longer though.
Yeah, the software token was only intended for testing purposes.[1] HID support is supposedly a goal for later this year.[2] There is also a third-party(?) add-on for hardware token support[3], but apparently it will stop working with FF 57 as it not was not written for WebExtensions.
(Disclaimer: not affiliated with Mozilla; I just check in on bug 1065729 every so often.)
