Examine source code of Custom Tab Icons

{
  "manifest_version": 3,
  "name": "Custom Tab Icons",
  "version": "1.0",
  "description": "Allow users to customize tab icons for easier recognition.",
  "icons": {
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e3d7b2a9-c5e8-4f9c-a7d3-b8e5f0b3c1a2}"
    }
  },
  "permissions": [
    "storage",
    "scripting",
    "activeTab"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}