Examine source code of Duplicate Tab Manager

{
  "manifest_version": 2,
  "name": "Duplicate Tab Manager",
  "version": "1.0",
  "description": "Close duplicate tabs and manage tab limits.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "ah9807073@gmail.com"
    }
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  }
}