Examine source code of Scroll To Top Button is

{
  "manifest_version": 2,
  "name": "Scroll To Top Button",
  "version": "1.0",
  "description": "Adds a floating button to scroll to top of the page",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ccbbefd6-b515-4a4c-b6da-4be6cef6dc0d}"
    }
  }
}