Examine source code of No Tab Left Behind

{
  "manifest_version": 2,
  "name": "No Tab Left Behind",
  "version": "0.0.9",
  "description": "Prevent duplicate tabs from dominating your browser window",
  "icons": {
    "16": "icons/store-logo-16.png",
    "32": "icons/store-logo-32.png",
    "48": "icons/store-logo-48.png",
    "64": "icons/store-logo-64.png",
    "96": "icons/store-logo-96.png",
    "128": "icons/store-logo-128.png"
  },
  "permissions": [
    "tabs",
    "webNavigation"
  ],
  "background": {
    "scripts": [
      "browser-polyfill.js",
      "lodash.js",
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/browser-action-light-32.png",
    "default_title": "No Tab Left Behind",
    "theme_icons": [
      {
        "light": "icons/browser-action-light-16.png",
        "dark": "icons/browser-action-dark-16.png",
        "size": 16
      },
      {
        "light": "icons/browser-action-light-32.png",
        "dark": "icons/browser-action-dark-32.png",
        "size": 32
      }
    ]
  }
}