Examine source code of Close New Duplicate Tabs

{
  "manifest_version": 2,
  "name": "Close New Duplicate Tabs",
  "version": "2.1",
  "description": "Closes a newly created tab if tab with the same URL is already open. Does not destroy your old tabs if you accidentally open a duplicate url.",
  "author": "Sunfur",
  "browser_specific_settings": {
    "gecko": {
      "id": "close-new-duplicate-tabs@sunfur.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "duplicate-detection.js",
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Close New Duplicate Tabs"
  },
  "permissions": [
    "tabs",
    "storage",
    "menus"
  ],
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": false
  }
}