Examine source code of Save Window With Tabs

{
  "manifest_version": 2,
  "name": "Tab Session Saver",
  "version": "1.0",
  "description": "Save and reopen tab groups by window.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e9eb0f44-aa94-46eb-bdf4-b7ae0d56f99d}"
    }
  }
}