Examine source code of On-Screen Time Tracker

{
  "manifest_version": 2,
  "name": "On-Screen Time Tracker",
  "version": "1.0",
  "description": "Track how much time you spend on screen.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "View your on-screen time"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a0ea66c7-2ec4-4056-a7a7-194069add242}"
    }
  }
}