Main repository: https://github.com/M-Reimer/midiinputprovider.
AMO: https://addons.mozilla.org/en-US/firefox/addon/midi-input-provider/
Hacking: Do a temporary install.
Building: make xpi
The target of this addon is, as the name suggests, to provide MIDI input to websites like piano learning platforms. That's what I want to use it for. I just didn't want to use Chrome for this task. To make this possible, this Addon implements just as much of the Web MIDI standard as required to hand over MIDI keyboards to websites.
If you need more, please don't waste your time with hacking for this Addon but have a closer look at this bug: Bug 836897: Implement the WebMIDI API.
This repository includes the required native application in the subdirectory "nativeapp". This native application is Linux only! and this is the only OS I directly support.
Feel free to create native applications for your OS, but please don't provide them as Pull-Request. Please host them in your own repository and create an issue with the link to your repository so I can link you.