Examine source code of Facebook Duck

{
  "manifest_version": 2,
  "name": "Facebook Duck",
  "version": "0.1.0",
  "description": "Add ducks on Facebook",
  "content_scripts": [
    {
      "css": [
        "styles.css"
      ],
      "matches": [
        "https://www.facebook.com/*"
      ],
      "js": [
        "main.js"
      ]
    }
  ],
  "icons": {
    "16": "/icons/icon16.png",
    "32": "/icons/icon32.png",
    "48": "/icons/icon48.png"
  }
}