Examine source code of AppStartTab

{
  "manifest_version": 3,
  "name": "AppStartTab",
  "short_name": "AppStartTab",
  "description": "Get app shortcuts on your new tab.",
  "version": "1.1.7",
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  },
  "icons": {
    "16": "img/icon16.png",
    "32": "img/icon32.png",
    "64": "img/icon64.png",
    "128": "img/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "appstarttab@example.com"
    }
  }
}