Examine source code of io game block

{
  "manifest_version": 2,
  "name": "NO IO GAMES",
  "version": "1.0",
  "description": "Blocking .io games ;)",
  "icons": {
    "48": "./icon.png"
  },
  "applications": {
    "gecko": {
      "id": "scretplayer@iogame.com",
      "strict_min_version": "45.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.io/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ]
}