Examine source code of auto close discarded tabs

{
  "manifest_version": 3,
  "name": "auto close discarded tabs",
  "version": "0.3.1",
  "description": "Close tabs which is discarded automatically.",
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "alarms",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{2718f57b-9ff4-4ecf-8aa3-f16d0184a62a}"
    }
  },
  "options_ui": {
    "page": "options.html"
  }
}