Examine source code of rarbg.thumbs

{
  "manifest_version": 2,
  "name": "rarbg.thumbs",
  "version": "1.0",
  "description": "Adiciona thumbnails a los enlaces de rarbg.com",
  "icons": {
    "48": "favicon.ico"
  },
  "content_scripts": [
    {
      "matches": [
        "*://rarbgweb.org/*"
      ],
      "js": [
        "rarbg.thumbs.js"
      ]
    }
  ]
}