Examine source code of Audible Volume Control

{
  "manifest_version": 3,
  "name": "Audible Audio Control",
  "version": "2.1.2",
  "description": "Adds a volume controller to the Audible webplayer.",
  "icons": {
    "48": "icons/volume.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "include_globs": [
        "https://www.audible.*/webplayer*"
      ],
      "js": [
        "audio-control.js"
      ],
      "css": [
        "audio-control.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6416fba2-1151-4e0b-ad65-1c36b3994ef1}"
    }
  }
}