Examine source code of DUCKPARK.IO

{
  "description": "The DUCKPARK.IO extension will add an icon in the speror's corner right from your browser. Add our extension to play in one click",
  "manifest_version": 2,
  "name": "DUCKPARK.IO",
  "version": "1.4",
  "homepage_url": "https://jogosonlineapps.com.br/apps/jogos-online/DUCKPARK-IO/GAME-DUCKPARK-IO.html",
  "icons": {
    "48": "icons/page-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/page-32.png"
  }
}