Examine source code of Mini Audio Peak Meter

{
  "manifest_version": 3,
  "name": "Peak Audio Meter",
  "version": "1.5",
  "browser_specific_settings": {
    "gecko": {
      "id": "peek-audio-meter@muniyoshid",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "description": "A toolbar audio meter for your browser tabs.",
  "permissions": [
    "scripting",
    "storage",
    "activeTab"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_title": "Audio Meter",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png"
    }
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "monitor.js"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  }
}