Examine source code of Notification Extension

{
  "manifest_version": 2,
  "name": "Notification Extension",
  "version": "1.0",
  "description": "Shows a notification every 10 seconds at the top of the screen for 1 second.",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "tolamironcenko@gmail.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}