Examine source code of Scroll Progress New

{
  "description": "Adds a scroll progress indicator to the current page",
  "manifest_version": 2,
  "name": "Scroll Progress New",
  "version": "1.4.5",
  "applications": {
    "gecko": {
      "id": "{aaf3d22a-ec17-430d-9075-dbcc2da2506f}"
    }
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_scripts/appearance.js",
        "content_scripts/scroll_progress.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options/options.html",
    "browser_style": true,
    "open_in_tab": true
  }
}