Examine source code of song typer

{
  "manifest_version": 3,
  "name": "song typer",
  "version": "0.1.1",
  "description": "turn typing into sequential MIDI note playback",
  "icons": {
    "16": "assets/icons/icon-16.png",
    "32": "assets/icons/icon-32.png",
    "48": "assets/icons/icon-48.png",
    "128": "assets/icons/icon-128.png"
  },
  "permissions": [
    "storage",
    "tabs"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "song-typer@hq.dev",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background/index.js"
    ]
  },
  "action": {
    "default_title": "song typer",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "assets/icons/icon-16.png",
      "32": "assets/icons/icon-32.png"
    }
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content/index.js"
      ],
      "run_at": "document_start"
    }
  ]
}