Examine source code of Header Editor

{
  "manifest_version": 3,
  "name": "Header Editor",
  "description": "Set custom request headers for matching URLs.",
  "version": "0.1.0",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "96": "icon/96.png",
    "128": "icon/128.png",
    "192": "icon/192.png"
  },
  "permissions": [
    "declarativeNetRequestWithHostAccess",
    "storage"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_icon": {
      "16": "icon/16.png",
      "32": "icon/32.png",
      "48": "icon/48.png",
      "96": "icon/96.png",
      "128": "icon/128.png"
    },
    "default_title": "Header Editor",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "header-editor@extension.local",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}