If you get a FireFox Warning: "MIDI access error: SecurityError: WebMIDI requires a site permission add-on to activate,"" that is a Firefox-specific restriction. Firefox requires the Jazz-Plugin or WebMIDI browser extension as a site permission add-on before it will grant Web MIDI access — it doesn't implement the Web MIDI API natively. The simplest fix is to use Chrome or Edge instead, which support Web MIDI natively with just a one-time permission prompt. Chrome will work perfectly with the IAC Driver.