Examine source code of restrict tab count

{
  "manifest_version": 3,
  "name": "tab-restrictor",
  "version": "1.0",
  "description": "restrict the number of tabs you can open",
  "action": {
    "default_popup": "popup.html",
    "default_icon": "icons/tab-48.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "icons": {
    "48": "icons/tab-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{05b06379-6fb1-4295-a6d3-76a63d80c760}"
    }
  }
}