Examine source code of Playlist Time Finder

{
  "manifest_version": 2,
  "name": "Playlist Time Finder",
  "version": "1.0",
  "description": "Shows the total time of a Youtube Playlist",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "scripting"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e933ea4f-8525-4965-90da-29dd084be027}"
    }
  }
}