Examine source code of Countdown Timer v5

{
  "manifest_version": 2,
  "name": "Countdown Timer",
  "version": "1.0",
  "description": "Set a countdown timer for your tasks and get notified when time's up.",
  "icons": {
    "48": "icons/timer-icon-48.png"
  },
  "permissions": [
    "notifications"
  ],
  "browser_action": {
    "default_icon": "icons/timer-icon-48.png",
    "default_popup": "popup.html",
    "default_title": "Countdown Timer"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{fda8280e-c5ab-4a14-a0c3-4d6b3ac94884}"
    }
  }
}