Examine source code of Goodlink

{
  "manifest_version": 2,
  "name": "Goodlink",
  "version": "1.0.2",
  "description": "A direct link to Goodreads from Amazon.",
  "browser_action": {
    "default_icon": {
      "16": "icons/grayed.png",
      "48": "icons/grayed@3x.png",
      "128": "icons/grayed@8x.png"
    }
  },
  "icons": {
    "16": "icons/grayed.png",
    "48": "icons/grayed@3x.png",
    "128": "icons/grayed@8x.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.amazon.in/*",
        "*://*.amazon.cn/*",
        "*://*.amazon.co.jp/*",
        "*://*.amazon.com.tr/*",
        "*://*.amazon.ae/*",
        "*://*.amazon.fr/*",
        "*://*.amazon.de/*",
        "*://*.amazon.it/*",
        "*://*.amazon.nl/*",
        "*://*.amazon.es/*",
        "*://*.amazon.co.uk/*",
        "*://*.amazon.ca/*",
        "*://*.amazon.com.mx/*",
        "*://*.amazon.com/*",
        "*://*.amazon.com.au/*",
        "*://*.amazon.com.br/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "permissions": [
    "tabs",
    "*://*.goodreads.com/*"
  ],
  "web_accessible_resources": [
    "*"
  ]
}