Examine source code of Scroll Progress

{
  "manifest_version": 3,
  "name": "Scroll Progress",
  "version": "1.0.0",
  "description": "Adds a slim progress bar to the top of every web page showing how far you have scrolled down the page.",
  "browser_specific_settings": {
    "gecko": {
      "id": "scrollprog@spfxext.com",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "64": "icons/icon-64.png",
    "128": "icons/icon-128.png"
  }
}