Examine source code of MP4 to MP3

{
  "manifest_version": 2,
  "default_locale": "en",
  "name": "MP4 to MP3",
  "version": "1.3.5",
  "description": "Use the MP4 to MP3 app to quickly and high-quality convert from mp4 to mp3, completely free of charge.",
  "permissions": [
    "activeTab",
    "http://*/*",
    "https://*/*"
  ],
  "background": {
    "scripts": [
      "src/pages/background/index.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_icon": "32.png"
  },
  "icons": {
    "32": "32.png",
    "48": "48.png",
    "64": "64.png",
    "128": "128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*",
        "<all_urls>"
      ],
      "js": [
        "src/pages/content/index.js"
      ],
      "run_at": "document_start",
      "css": []
    }
  ],
  "web_accessible_resources": [
    "assets/js/*.js",
    "assets/css/*.css",
    "assets/svg/*.svg",
    "icon.svg",
    "blob/*"
  ],
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "browser_specific_settings": {
    "gecko": {
      "id": "{48063e66-940b-4b42-b212-a7051d945d44}"
    }
  }
}