Examine source code of Spotify Number Seek

{
  "manifest_version": 2,
  "name": "Spotify Number Seek",
  "version": "1.0",
  "description": "Press 0–9 to seek to that % of the current Spotify track",
  "author": "Mahmoud Raafat",
  "icons": {
    "48": "logo_48.png",
    "96": "logo_96.png",
    "128": "logo_128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://open.spotify.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "spotify-number-seek@mahmoudraafat.dev",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}