Greetings Firefox user!
In order to use the Web MIDI capabilities of this demo, you will need to install an add-on that enables it to request the permissions needed to access your MIDI devices.
Once you've downloaded the add-on and granted the permissions, please refresh the page to activate Web MIDI in the demo.
Thanks for your cooperation. You can download the add-on here.
If you're not using the local synth, you need to connect this output to a MIDI synth like FluidSynth, TiMidity, or DX7 Synth