Examine source code of FueraLaLiga

{
  "manifest_version": 2,
  "name": "FueraLaLiga",
  "version": "0.3",
  "description": "Fuera La Liga de tu Twitter.",
  "icons": {
    "16": "assets/icon_16.png",
    "32": "assets/icon_32.png",
    "48": "assets/icon_48.png",
    "96": "assets/icon_96.png",
    "128": "assets/icon_128.png"
  },
  "page_action": {
    "default_icon": {
      "16": "assets/icon_16.png",
      "32": "assets/icon_32.png",
      "48": "assets/icon_48.png",
      "96": "assets/icon_96.png",
      "128": "assets/icon_128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.twitter.com/*"
      ],
      "js": [
        "script.js"
      ]
    }
  ]
}