Examine source code of digi4school to pdf

{
  "manifest_version": 2,
  "name": "digi4school to pdf",
  "version": "1.5",
  "author": "strukteon",
  "description": "Converts digi4school books to pdf so they can be used offline.",
  "homepage_url": "https://github.com/strukteon/digi4school-to-pdf",
  "icons": {
    "32": "assets/icon-32.png",
    "64": "assets/icon-64.png",
    "128": "assets/icon-128.png",
    "512": "assets/icon-512.png"
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "assets/icon-64.png",
    "default_title": "digi4school to pdf",
    "default_popup": "popup/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*/ebook/*"
      ],
      "js": [
        "libraries/browser-polyfill.min.js",
        "scripts/d4s_detection.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "libraries/browser-polyfill.min.js",
      "scripts/background.js"
    ]
  }
}