Examine source code of ChronoTick

{
  "manifest_version": 2,
  "name": "Countdown Timer",
  "version": "1.0.0",
  "description": "Countdown timer with popup-bound sound",
  "permissions": [
    "alarms",
    "notifications",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "web_accessible_resources": [
    "sounds/tick.mp3",
    "sounds/alarm.mp3"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{42988f29-0639-4e19-8877-77245b8c8385}"
    }
  }
}