Examine source code of Close After Last Tab

{
  "manifest_version": 2,
  "name": "Close After Last Tab",
  "version": "1.1resigned1",
  "description": "Close window after last tab has been closed. \n(Chrome-like behaviour of closing last tab) \n\n1. Please go to Options and set: \nWhen Firefox starts, Show your windows and tabs from last time. \n\n2. Go to about:config, set \nbrowser.tabs.closeWindowWithLastTab = false",
  "author": "YK Leung",
  "homepage_url": "https://www.facebook.com/delphisnote",
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{fd259e24-757c-4edd-ae36-a2005578f1ad}"
    }
  }
}