Examine source code of Duplicate Tab Closer

{
  "manifest_version": 2,
  "name": "Duplicate Tab Closer",
  "version": "1.0",
  "description": "Closes duplicate tabs across all windows.",
  "icons": {
    "48": "icons/duplicate-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/duplicate-48.png",
    "default_title": "Close Duplicate Tabs"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{602b7ec0-8225-474d-8baf-bd242dfda21c}"
    }
  }
}