Examine source code of Typewriter Marker

{
  "manifest_version": 2,
  "name": "Typewriter Marker",
  "version": "1.0",
  "description": "Ersetzt den grauen Hintergrund auf typewriter.at durch einen farbigen Strich vor dem aktuellen Buchstaben.",
  "permissions": [
    "storage",
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://at4.typewriter.at/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.svg"
    },
    "default_title": "Typewriter Marker"
  },
  "icons": {
    "48": "icon.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "typewriter-marker@extension",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}