Examine source code of Playlist Time Calculator

{
  "manifest_version": 2,
  "name": "YouTube Playlist Duration",
  "description": "Displays the total duration of YouTube playlists and estimated time needed for different playback speeds.",
  "version": "1.0",
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "contentScript.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "applications": {
    "gecko": {
      "id": "your-extension-id@yourdomain.com",
      "strict_min_version": "42.0"
    }
  }
}