Examine source code of GoToGoodReads

{
  "manifest_version": 2,
  "name": "GoToGoodReads",
  "version": "1.0",
  "description": "Adds Go to GoodReads button on amazon",
  "icons": {
    "48": "icon-48.png",
    "96": "icon-96.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://www.amazon.com/*",
        "https://www.amazon.in/*",
        "https://www.amazon.co.uk/*",
        "https://www.amazon.jp/*",
        "https://www.amazon.de/*",
        "https://www.amazon.ca/*",
        "https://www.amazon.fr/*",
        "https://www.amazon.cn/*",
        "https://www.amazon.it/*",
        "https://www.amazon.com.au/*"
      ],
      "js": [
        "addGoodreadsButton.js"
      ]
    }
  ]
}