Examine source code of YouTube Language Trainer

{
  "manifest_version": 2,
  "name": "YouTube Language Trainer",
  "version": "1.0",
  "description": "Highlight selected words/phrases in YouTube subtitles for language learning.",
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{bd2c97f8-5164-4015-aa37-0f521df4cf31}"
    }
  }
}