Examine source code of Spotify Smooth Transition

{
  "manifest_version": 3,
  "name": "Spotify Smooth Transition",
  "version": "1.0",
  "description": "Fait un fondu de volume (fade-out et fade-in) sur le lecteur web Spotify.",
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "spotify-smooth-transition@ton-domaine.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}