Woah this is a MASSIVE deviation from FF's previous philosophy on allowing WebSerial. This is a GOOD thing!
And maybe we'll get web bluetooth too.
Bring up WebSerial and WebUSB and oh no, all of a sudden, my 'document browser should not be accessing hardware' - yes we get it, you think the web is a collection of documents and are technically - in the most strictest sense possible correct. Hyper TEXT Transfer Protocol and all that.
Of course I've been watching Netflix and YouTube on my Firefox 'document browser' for years, because if I couldn't then there would literally no hope of anyone using Firefox in the real world, but WebUSB and WebSerial people are nerds who we can argue the toss about document browsers with and prove wrong.