Examine source code of Custom Web Clock

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "version": "0.4.3",
  "description": "__MSG_extensionName__",
  "browser_action": {
    "default_title": "clock",
    "browser_style": true,
    "default_popup": "popup/popup.html"
  },
  "icons": {
    "48": "clock.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "js/lego_cale.js",
        "lib/react-16.13.1.umd.min.js",
        "lib/react-dom-16.13.1.umd.min.js",
        "js/utils.js",
        "js/widgets.js",
        "js/clock.js",
        "js/alert.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "js/font.js",
      "js/utils.js",
      "js/background.js"
    ]
  },
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": true
  },
  "permissions": [
    "storage",
    "tabs",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6b26c880-7687-4f21-9ffc-26aa9fa9ccd8}"
    }
  }
}