Examine source code of Countdown Timer

{
  "manifest_version": 2,
  "name": "Countdown Timer",
  "version": "2.3.1.3",
  "description": "Track how long until your deadlines, trips and celebrations. Create multiple date-and-time countdowns, watch each one update every second, and get a badge for the nearest event plus a notification once it is due.",
  "icons": {
    "32": "assets/icon-32.png",
    "48": "assets/icon-48.png",
    "64": "assets/icon-64.png",
    "96": "assets/icon-96.png",
    "128": "assets/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c9d6cc12-c108-44eb-8801-643223f5d5f0}",
      "strict_min_version": "101.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "storage",
    "alarms",
    "notifications"
  ],
  "background": {
    "scripts": [
      "app/background.js"
    ]
  },
  "browser_action": {
    "default_title": "Countdown Timer",
    "default_popup": "app/popup.html",
    "default_icon": {
      "32": "assets/icon-32.png",
      "48": "assets/icon-48.png",
      "64": "assets/icon-64.png"
    }
  }
}