Examine source code of Subnet Calc

{
  "manifest_version": 2,
  "name": "Subnet Calc",
  "version": "1.1",
  "description": "Calculate subnet mask network and broadcast address",
  "browser_specific_settings": {
    "gecko": {
      "id": "{72eca7f4-2f74-4506-bbf7-aa8cf3e411db}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "icons/s16.png",
    "48": "icons/s48.png"
  },
  "browser_action": {
    "default_popup": "view/index.html",
    "default_icon": {
      "16": "icons/s16.png",
      "48": "icons/s48.png"
    }
  },
  "background": {
    "scripts": [
      "core/worker.js"
    ]
  },
  "permissions": []
}