Examine source code of Promo Countdown Tab

{
  "manifest_version": 2,
  "name": "Promo Countdown Tab",
  "version": "1.0",
  "description": "Display a countdown timer for promotions.",
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "promocountdown@example.com",
      "strict_min_version": "91.0"
    }
  }
}