Examine source code of Reading Progress Bar

{
  "manifest_version": 2,
  "name": "Reading Progress Bar",
  "version": "2.0",
  "description": "Displays a progress bar on all websites to show reading progress. This extension does not collect or store user data.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{27a645c8-e416-4ba0-a4ad-05154114879b}"
    }
  }
}