Examine source code of Time Calculator

{
  "manifest_version": 2,
  "name": "Time Calculator",
  "version": "1.1",
  "description": "Perform simple time calculations.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "32": "icons/clock-icon-48.png"
    }
  },
  "icons": {
    "32": "icons/clock-icon-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{67cc08ba-058a-4133-8c63-915d1d44a176}"
    }
  }
}