Examine source code of Close duplicate tabs

{
  "manifest_version": 2,
  "name": "Close duplicate tabs",
  "version": "0.3resigned1",
  "browser_action": {
    "default_title": "Close duplicate tabs",
    "default_icon": {
      "48": "icon.svg"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icon.svg"
  },
  "permissions": [
    "cookies",
    "notifications",
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{42f2b93e-6280-464d-be04-571237816f70}"
    }
  }
}