Examine source code of Youtube Thumbnail Grabber

{
  "manifest_version": 2,
  "name": "Youtube Thumbnail Grabber",
  "description": "Adds context menu options to open Youtube thumbnails in new tabs.",
  "author": "Kyagara",
  "default_locale": "en",
  "version": "0.2",
  "homepage_url": "https://github.com/Kyagara/thumbnail-grabber-extension",
  "background": {
    "scripts": [
      "browser-polyfill-min.js",
      "background.js"
    ]
  },
  "permissions": [
    "activeTab",
    "contextMenus"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e691fc38-1537-4507-b177-78c9087bb1e4}"
    }
  }
}