Examine source code of Youtube Rick Roller

{
  "manifest_version": 2,
  "name": "Youtube Rick Roller",
  "version": "1.2.0",
  "description": "This extention will never going to give you up ;) You can rickroll your friends by installing this on their browsers. ",
  "icons": {
    "48": "images/48x48.png",
    "128": "images/128x128.png",
    "512": "images/512x512.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "contentScript.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}