Examine source code of Etherscan

{
  "name": "Etherscan",
  "description": "View the current gas fees and the latest block number with a single click.",
  "version": "1.0.2",
  "manifest_version": 2,
  "icons": {
    "128": "icons/128.png"
  },
  "browser_action": {
    "default_popup": "index.html",
    "default_icon": {
      "128": "icons/128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7e3567ef-cef6-4475-b695-6d699e5a683a}"
    }
  }
}