Examine source code of Better tab rotate

{
  "manifest_version": 2,
  "name": "Better tab rotate",
  "version": "0.2",
  "description": "rotate tabs",
  "icons": {
    "48": "icons/tab-rotate.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "eemelilari@gmail.com"
    }
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/tab-rotate-disabled.png"
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "permissions": [
    "idle",
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "rotate.js"
    ],
    "persistent": true
  }
}