Examine source code of Reading Progress Tracker

{
  "manifest_version": 2,
  "name": "Reading Progress Tracker",
  "version": "1.0",
  "description": "Displays a reading progress bar at the bottom of the webpage to help users track how much content is left.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{50eb9990-ac2c-4664-99aa-e0e15ce8e46e}"
    }
  }
}