Examine source code of Tab Timeout Closer

{
  "author": "igorlogius",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_area": "navbar"
  },
  "description": "Automatically close tabs which have not been accessed for a time",
  "icons": {
    "256": "icon.png"
  },
  "manifest_version": 2,
  "name": "Tab Timeout Closer",
  "permissions": [
    "contextualIdentities",
    "cookies",
    "bookmarks",
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "options_ui": {
    "page": "options.html"
  },
  "incognito": "not_allowed",
  "version": "1.8.26",
  "browser_specific_settings": {
    "gecko": {
      "id": "{9032a9a1-e9c8-409f-a15a-920ca63d3920}"
    }
  }
}