Examine source code of Close Last Tab

{
  "manifest_version": 2,
  "name": "Close Last Tab",
  "version": "1.3",
  "description": "When the last tab is closed it closes the window and does not restore that tab at the next startup. Requires that browser.tabs.closeWindowWithLastTab is set to false in about:config.",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs"
  ]
}