Examine source code of Typing Piano

{
  "manifest_version": 2,
  "name": "Typing Piano",
  "version": "1.0.0",
  "description": "Gõ phím = chơi piano. Có chế độ silent chỉ ghi lại.",
  "permissions": [
    "storage",
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_title": "Toggle Silent Mode"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "128": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "typing-piano@addon",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}