Examine source code of HeaderNinja

{
  "manifest_version": 3,
  "name": "HeaderNinja",
  "version": "1.0.0",
  "description": "Add or override HTTP request headers on outgoing requests, with an optional URL filter per rule. No tracking, no data collection.",
  "browser_specific_settings": {
    "gecko": {
      "id": "headerninja@byteferret",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "declarativeNetRequest",
    "storage"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "action": {
    "default_title": "HeaderNinja",
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/icon.svg",
      "96": "icons/icon.svg"
    }
  },
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  }
}