Examine source code of Device Emulator

{
  "manifest_version": 2,
  "name": "Device Emulator",
  "version": "1.0.0",
  "description": "Override the browser User-Agent header for all requests. Choose from desktop, mobile, and bot presets or enter custom.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{5e98146e-b4e0-43d3-869a-48326ed95b41}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "96": "icons/icon96.png",
      "128": "icons/icon128.png"
    },
    "default_title": "Device Emulator",
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "96": "icons/icon96.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  }
}