Examine source code of Reading Progress Bar PRO

{
  "manifest_version": 2,
  "name": "Reading Progress Bar",
  "version": "1.0",
  "description": "Shows a customizable reading progress bar as you scroll through content",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    },
    "default_title": "Reading Progress Bar",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{37a23c94-0366-455f-8154-55bb99adad6b}"
    }
  }
}