Examine source code of Simple Timezone Clock

{
  "manifest_version": 2,
  "name": "Simple Timezone Clock",
  "version": "1.1",
  "author": "Slaven Sladakovic",
  "description": "A simple timezone clock extension for Firefox",
  "icons": {
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_icon": "timezone-clock.png",
    "default_popup": "timezone-clock.html"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{72e8a5b7-93ec-48c1-9b13-d4d8ea9adf9b}"
    }
  }
}