Examine source code of Reading Speed Tracker12

{
  "manifest_version": 2,
  "name": "Reading Speed Tracker",
  "version": "1.0",
  "description": "Track reading speed per paragraph and display words per minute (WPM).",
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{5a584119-cab7-42d5-b93e-062ac5b85db9}"
    }
  }
}