Examine source code of Movie Rating Sync

{
  "manifest_version": 2,
  "name": "Movie Ratings Sync",
  "name:ru": "Синхронизация Кинооценок",
  "version": "1.0",
  "description": "Sync movie ratings across Kinopoisk, IMDb, Letterboxd and more",
  "description:ru": "Синхронизируйте оценки фильмов между Kinopoisk, IMDb и другими сервисами",
  "author": "Smokelweiss",
  "homepage_url": "https://github.com/Smokelweiss/MovieRatingSync",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.kinopoisk.ru/*",
        "https://www.imdb.com/*",
        "https://letterboxd.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "https://www.kinopoisk.ru/*",
    "https://graphql.kinopoisk.ru/*",
    "https://www.imdb.com/*",
    "https://api.graphql.imdb.com/*",
    "https://letterboxd.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "movie-ratings-sync@smokelweiss",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}