Examine source code of YouTube Screenshot

{
  "manifest_version": 2,
  "name": "YouTube Screenshot",
  "version": "3.0",
  "description": "Take screenshots of YouTube videos",
  "applications": {
    "gecko": {
      "id": "youtube-screenshot@emple.com"
    }
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "permissions": [
    "*://www.youtube.com/*"
  ]
}