Examine source code of Youtube Video Thumb

{
  "manifest_version": 2,
  "name": "Yutube Thumb",
  "description": "This extension generate thumbnail image for youtube and Facebook videos. Now generate thumbnail from a embedded youtube/facebook webpage.",
  "version": "2.1",
  "background": {
    "scripts": [
      "back.js"
    ]
  },
  "icons": {
    "64": "icon.png",
    "128": "icon128.png",
    "512": "icon512.png"
  },
  "browser_action": {
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "yutube.js"
      ],
      "all_frames": true
    }
  ],
  "permissions": [
    "tabs"
  ]
}