Examine source code of Notification Sound

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "description": "__MSG_extensionDescription__",
  "default_locale": "en",
  "applications": {
    "gecko": {
      "id": "@notification-sound",
      "strict_min_version": "63.0a1"
    }
  },
  "author": "freaktechnik",
  "version": "1.4.2resigned1",
  "icons": {
    "48": "images/Notification_Sound_Icon.svg",
    "96": "images/Notification_Sound_Icon.svg"
  },
  "background": {
    "scripts": [
      "scripts/stored-sound.js",
      "scripts/background.js"
    ]
  },
  "options_ui": {
    "page": "pages/options.html",
    "browser_style": true
  },
  "permissions": [
    "storage",
    "management",
    "downloads",
    "menus",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "scripts/content-script.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ]
}