Examine source code of WhatsApp Contacts Saver

{
  "manifest_version": 2,
  "name": "__MSG_appName__",
  "description": "__MSG_appDescription__",
  "version": "0.0.1",
  "icons": {
    "16": "icons/16.png",
    "32": "icons/32.png",
    "48": "icons/48.png",
    "64": "icons/64.png",
    "128": "icons/128.png"
  },
  "default_locale": "en",
  "permissions": [
    "storage",
    "tabs"
  ],
  "web_accessible_resources": [
    "client.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      },
      "id": "whatsapp-contacts-saver@muzammil.work"
    }
  },
  "browser_action": {
    "default_title": "Popup",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.whatsapp.com/*"
      ],
      "run_at": "document_idle",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}