Examine source code of Don't Close Last Tab

{
  "manifest_version": 2,
  "name": "Don't Close Last Tab",
  "short_name": "Don't Close Last Tab",
  "description": "If there are pinned tabs, keep one blank tab open when closing the last normal one.",
  "version": "1.1.1resigned1",
  "applications": {
    "gecko": {
      "id": "dont-close-last@mozilla.kewis.ch"
    }
  },
  "icons": {
    "16": "images/addon.svg",
    "32": "images/addon.svg",
    "48": "images/addon.svg",
    "128": "images/addon.svg"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "options_ui": {
    "page": "options/options.html",
    "browser_style": true
  },
  "background": {
    "scripts": [
      "background/background.js"
    ]
  }
}