Examine source code of Time Calculator

{
  "manifest_version": 2,
  "name": "Time Calculator",
  "version": "1.0",
  "description": "Calculate work time between start and end times",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Time Calculator"
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d7178939-1038-438f-8d58-b0174c580f80}"
    }
  }
}