WebSerial and WebUSB are the best thing to happen to browsers since sliced bread. Just because you can't see why it's amazing that users won't need to give some random, badly supported driver SYSTEM/root privileges to run their specialized hardware -- encompassing hobbyist, educational and professional uses -- doesn't mean it's not obviously useful, and Mozilla's stance on keeping it out of Firefox will just harm their market share in these area -- education probably being the most hurtful.

From what I gather here, XSLT's functionality OTOH is easily replaced, and unlike the useful hardware support you're raging against, is a behemoth to support.