Following that link on Firefox ESR led me to the following Bugzilla issue about a 10+ year old issue with Firefox not implementing Web-MIDI which was just resolved two months ago:

https://bugzilla.mozilla.org/show_bug.cgi?id=836897

Needless to say, I went down the rabbit hole a bit. :)

I found it weirdly interesting to see the advocacy among musicians and music apps (I dabble with synths, and MIDI is pretty important) and the dismissal of the issue by a few maintainers.