Great idea! I see this was being investigated by Mozilla several years ago but it didn't progress to release.
It is hard to get Hi-Res audio streams via WASAPI exclusive mode through any browser currently. If we want to take advantage of the Hi-Res streams out there such as BBC Radio 3, or Mother Earth it doesn't seem to be possible currently - I would have thought one of them would have done it. In fact it seems that Chrome used to do it, but no more.
This would be a great high-end niche for FireFox to fill - and advertise as such.