Examine source code of Onleihe Checker

{
  "manifest_version": 2,
  "name": "Onleihe Checker",
  "version": "1.2",
  "description": "Check book availability in German digital libraries (Onleihe) while browsing Amazon.de and Goodreads",
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "author": "Veliko Kardziev",
  "permissions": [
    "storage",
    "activeTab",
    "tabs",
    "webNavigation",
    "https://www.amazon.de/*",
    "https://amazon.de/*",
    "https://www.goodreads.com/*",
    "https://goodreads.com/*",
    "https://*.onleihe.de/*",
    "https://*.onleihe.net/*",
    "https://*.onleihe.ch/*",
    "https://*.onleihe.at/*",
    "https://*.onleihe.be/*",
    "https://*.onleihe.fr/*",
    "https://*.onleihe.it/*",
    "https://*.onleihe.lu/*",
    "https://*.onleihe.li/*",
    "https://www.ostalb-onleihe.de/*",
    "https://ostalb.onleihe.de/*",
    "https://www.metropolbib.de/*",
    "https://www.franken-onleihe.de/*",
    "https://www.leo-sued.de/*",
    "https://www.leo-nord.de/*",
    "https://www.enio24.de/*",
    "https://www.digibobb.de/*",
    "https://www.biblioload.de/*",
    "https://www.biblioplus-digital.de/*",
    "https://www.e-medien-franken.de/*",
    "https://www.e-ausleihe-franken.de/*",
    "https://www.emedienbayern.de/*",
    "https://www.ebook.baden.ch/*",
    "https://www.elbe-elster-bibnet.de/*",
    "https://hessen.onleihe.de/*",
    "https://voebb.onleihe.de/*",
    "https://oberlausitz.onleihe.de/*",
    "https://www.onleihe-oberlausitz.de/*",
    "http://*.onleihe.de/*",
    "http://*.onleihe.net/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Onleihe Checker - Check book availability",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.amazon.de/*/dp/*",
        "https://amazon.de/*/dp/*",
        "https://amazon.de/dp/*",
        "https://www.amazon.de/dp/*",
        "https://www.amazon.de/gp/product/*",
        "https://amazon.de/gp/product/*",
        "https://www.goodreads.com/book/show/*",
        "https://goodreads.com/book/show/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "web_accessible_resources": [
    "libraries.json",
    "locales.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e5bab5d1-a259-4ed7-b89d-078baa3fdeb6}"
    }
  }
}