Examine source code of Keyboard ASMR

{
  "manifest_version": 2,
  "name": "Keyboard ASMR",
  "version": "1.4",
  "description": "Add satisfying, synthesized key sounds as you type on any page. Choose a soft pop, typewriter, or mechanical style, set the volume, and try it right in the popup. Sounds are generated live, no audio files.",
  "icons": {
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c14ecb69-daf5-4e75-bdd2-abc6a3492468}",
      "strict_min_version": "101.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/asmr.js"
      ],
      "run_at": "document_idle",
      "all_frames": false
    }
  ],
  "browser_action": {
    "default_title": "Keyboard ASMR",
    "default_popup": "src/popup.html",
    "default_icon": {
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "64": "icons/icon-64.png"
    }
  }
}