Examine source code of Load timer

{
  "name": "Page load time",
  "version": "4.0",
  "manifest_version": 3,
  "description": "Displays page load time in the toolbar",
  "background": {
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  },
  "action": {
    "default_icon": "stopwatch22.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "browser-polyfill.min.js",
        "performance.js"
      ]
    }
  ],
  "permissions": [
    "activeTab",
    "storage"
  ],
  "icons": {
    "16": "stopwatch16.png",
    "48": "stopwatch48.png",
    "128": "stopwatch128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{da981873-0eb3-4e62-9dcf-fcb6c349a676}"
    }
  }
}