Examine source code of Close Ungrouped Tabs

{
  "manifest_version": 2,
  "name": "Close Ungrouped Tabs",
  "version": "1.0",
  "description": "Closes all tabs that are not in any tab group.",
  "permissions": [
    "tabs",
    "tabGroups"
  ],
  "browser_action": {
    "default_title": "Close ungrouped tabs",
    "default_icon": {
      "16": "icon.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ccb5e14d-08c4-44ef-b144-4600a091ad1a}"
    }
  }
}