Examine source code of User-Agent Header Manager

{
  "manifest_version": 2,
  "name": "User-Agent Header Manager",
  "version": "1.0.1",
  "description": "Customize User-Agent and other HTTP headers globally or per-site",
  "permissions": [
    "storage",
    "activeTab",
    "tabs",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "options_page": "options.html",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "user-agent-manager@plainsimple.dev",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}