Devices that offer serial interfaces often expose powerful, low-level functions over the interface with little or no authentication. Exposing that sort of capability to the web without adequate safeguards presents a significant threat to those devices. A user deliberately installing a site-specific add-on may be adequate, given sufficiently understandable consent copy.
For those not wanting go search:
Mozilla’s Position
Devices that offer serial interfaces often expose powerful, low-level functions over the interface with little or no authentication. Exposing that sort of capability to the web without adequate safeguards presents a significant threat to those devices. A user deliberately installing a site-specific add-on may be adequate, given sufficiently understandable consent copy.
Seems reasonable to me.