What a user agent is
Every request your browser makes includes a user agent header that names the browser, its engine and the operating system. Sites use it for compatibility and statistics. Because many browsers pretend to be others for compatibility, the string looks cluttered: almost every browser still starts with Mozilla/5.0. Modern Chromium browsers also expose cleaner data through User-Agent Client Hints, which this page uses when available.
Keeping your browser up to date
Browsers update themselves automatically, but only after a restart. If the version shown here is several releases behind, open the browser's "About" page to install the update; it fixes security issues that websites cannot protect you from.