Examine source code of Add to Spotify

{
  "manifest_version": 2,
  "name": "Add to Spotify",
  "version": "1.0.0",
  "description": "Add YouTube songs directly to your Spotify playlists with one click.",
  "icons": {
    "16": "assets/icon16.png",
    "48": "assets/icon48.png",
    "128": "assets/icon128.png"
  },
  "permissions": [
    "storage",
    "identity",
    "https://www.youtube.com/*",
    "https://accounts.spotify.com/*",
    "https://api.spotify.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/watch*"
      ],
      "js": [
        "utils/storage.js",
        "utils/spotify_api.js",
        "content/song_detector.js",
        "content/toast.js",
        "content/modal.js",
        "content/content_script.js"
      ],
      "css": [
        "styles/button.css",
        "styles/modal.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "assets/icon16.png",
      "48": "assets/icon48.png",
      "128": "assets/icon128.png"
    }
  },
  "web_accessible_resources": [
    "assets/spotify_logo.svg"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "add-to-spotify@example.com",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}