Examine source code of Amazon product checker

{
  "manifest_version": 2,
  "name": "Amazon product checker",
  "description": "Checks every 5min if a product is available",
  "author": "trc",
  "version": "1.0",
  "icons": {
    "128": "icon-128.png"
  },
  "permissions": [
    "https://*.amazon.com/*",
    "https://*.amazon.fr/*",
    "https://*.amazon.uk/*",
    "https://*.amazon.pl/*",
    "https://*.amazon.es/*",
    "https://*.amazon.it/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.amazon.com/*",
        "https://*.amazon.fr/*",
        "https://*.amazon.uk/*",
        "https://*.amazon.pl/*",
        "https://*.amazon.es/*",
        "https://*.amazon.it/*"
      ],
      "js": [
        "injected.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icon-128.png",
    "default_popup": "popup.html"
  }
}