Examine source code of Volume booster

{
  "manifest_version": 3,
  "browser_specific_settings": {
    "gecko": {
      "id": "volume-booster@addon-firefox",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "name": "__MSG_extName__",
  "description": "__MSG_description__",
  "version": "2.2.0",
  "default_locale": "en",
  "icons": {
    "64": "assets/icon-64.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "scripting"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_title": "__MSG_extName__",
    "default_icon": {
      "16": "assets/icon-16.png",
      "32": "assets/icon-32.png",
      "48": "assets/icon-48.png",
      "128": "assets/icon-128.png"
    }
  },
  "background": {
    "scripts": [
      "bg.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "all_frames": true,
      "run_at": "document_start"
    }
  ],
  "commands": {
    "_execute_action": {}
  },
  "options_page": "./options.html",
  "web_accessible_resources": [
    {
      "resources": [
        "assets/*",
        "audio.js"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "content_security_policy": {
    "extension_pages": "script-src 'self'; object-src 'self'; frame-src *;"
  }
}