Examine source code of Viewport Inspector

{
  "manifest_version": 2,
  "name": "Extension",
  "version": "2.0.1",
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      },
      "id": "{801ff754-4917-437b-860c-50f43273998f}"
    }
  },
  "background": {
    "scripts": [
      "assets/js/background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_title": "Extension",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "permissions": [
    "tabs",
    "clipboardRead"
  ],
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  }
}