Examine source code of Christmas Clock

{
  "manifest_version": 2,
  "name": "Countdown Timer",
  "version": "1.1",
  "description": "Displays a countdown to Christmas.",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png",
      "48": "icon.png",
      "128": "icon.png"
    }
  },
  "icons": {
    "16": "icon.png",
    "48": "icon.png",
    "128": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6aad6825-c75b-4b1a-9b92-9b51b025b45f}"
    }
  }
}