Examine source code of clock-extension

{
  "manifest_version": 2,
  "name": "clock-extension",
  "short_name": "Shows a digital or analogue clock on new tab",
  "version": "1.5.1",
  "description": "Replaces newtab with analogue clock",
  "homepage_url": "https://iegik.github.io/clock-extension/",
  "icons": {
    "48": "icons/icon-48.png",
    "72": "icons/icon-72.png",
    "96": "icons/icon-96.png",
    "144": "icons/icon-144.png",
    "168": "icons/icon-168.png",
    "192": "icons/icon-192.png"
  },
  "chrome_url_overrides": {
    "newtab": "background.html"
  },
  "options_ui": {
    "page": "options.html"
  },
  "web_accessible_resources": [
    "data/theme.html",
    "data/theme.svg"
  ],
  "permissions": [
    "storage",
    "idle"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5f04c647-da4a-4ae0-8a9b-cfc9df81a2d0}"
    }
  }
}