Examine source code of Tab Cleaner

{
  "manifest_version": 2,
  "name": "Close all background tabs",
  "version": "1.0.1",
  "description": "An extension to close all inactive tabs.",
  "author": "Bozidar Atanasovski",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "48": "/icons/icon-48.png"
    },
    "default_popup": "popup.html",
    "default_title": "Close Tabs"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{84cc28f3-ceca-40e6-adf9-dc02a82053af}"
    }
  }
}