Examine source code of abcjs player mod

{
  "manifest_version": 3,
  "name": "abcjs player mod",
  "description": "Extra options for playing midi on adcjs-based web player",
  "version": "1.2.0",
  "author": "DaveRo",
  "browser_specific_settings": {
    "gecko": {
      "id": "abcjs_play_extras@davero.addons.mozilla.org",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    },
    "gecko_android": {}
  },
  "content_scripts": [
    {
      "matches": [
        "https://editor.drawthedots.com/*",
        "https://michaeleskin.com/*"
      ],
      "js": [
        "abcjs_play_mod.js"
      ]
    }
  ]
}