Examine source code of Page Scroll Progress

{
  "manifest_version": 2,
  "name": "Page Scroll Progress",
  "version": "1.0.0",
  "description": "Visual progress bar showing how much of the webpage you have scrolled through",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Page Scroll Progress",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "progress.css"
      ],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ff21a106-d6be-4966-8383-fd307de5643f}"
    }
  }
}