Examine source code of Relative Tab Numbers

{
  "manifest_version": 3,
  "name": "Relative Tab Numbers",
  "description": "Show tab numbers relative to the active tab",
  "version": "0.1.2",
  "permissions": [
    "tabs",
    "activeTab",
    "scripting"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "icons": {
    "32": "icons/icon32.png"
  },
  "background": {
    "scripts": [
      "main.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "relative-tab-numbers@addons.mozilla.org"
    }
  }
}