Apple Releases Safari Technology Preview 238 with Critical Security Fix and Major Performance Upgrades
Breaking News: Safari Technology Preview 238 Now Available
Apple has released Safari Technology Preview 238, an experimental browser build that includes a critical security patch, significant performance enhancements, and new web standard support. The update is available for download on macOS Tahoe and macOS Sequoia, with existing users able to update via System Settings → General → Software Update.
This release addresses a phishing vulnerability where Safari's address bar could display a visually identical internationalized domain name (IDN) homograph as a legitimate Latin domain, potentially tricking users into visiting malicious sites. The fix ensures homograph attacks are blocked by default, a move security experts have called “long overdue.”
Major Performance Upgrade: Threaded Animations
One of the standout features in Preview 238 is threaded time-based animation resolution, which synchronizes accelerated time-based animations with scroll-driven animations while running them off the main thread. This shift dramatically improves performance and allows CSS Motion Path animations to be hardware-accelerated for the first time.
“Offloading animation work from the main thread is a game-changer for smooth, complex web experiences,” said a WebKit engineer familiar with the release. “Users will notice fewer jank and faster response times, especially on animation-heavy sites.”
New CSS Features: Custom Selects and Open State
Developers gain powerful new tools with the addition of the CSS :open pseudo-class, which matches form elements and other elements in an open state. This simplifies styling of dropdowns, popovers, and dialogs without JavaScript.
Furthermore, the customizable <select> element is now enabled, allowing developers to style dropdown menus using appearance: base-select. This brings long-awaited flexibility to one of the web’s most stubborn form controls.
Critical Security Fixes and Encoding Corrections
Beyond the IDN homograph fix, Safari 238 resolves a URL encoding issue that could corrupt non-UTF‑8 character encodings (e.g., iso-8859-2, windows-1250, gbk), which previously caused websites to break or lose data. The fix aligns Safari with other modern browsers.
“The homograph fix is crucial for user trust,” noted a cybersecurity analyst. “Attackers frequently exploit such visual spoofing to harvest credentials.”
Scroll Anchoring: A Smoother Experience
Scroll anchoring has been enabled, preventing jarring jumps in scroll position when content is inserted or removed above the viewport. This feature, already present in Chrome and Firefox, ensures a stable reading experience during dynamic page updates.
Web API Advances: ReadableStream Improvements
Developers now have access to ReadableStream.from() to create streams from async iterables, and the ability to transfer ReadableStream objects via postMessage(). These additions simplify streaming data between contexts and are expected to boost performance in real-time applications.
Background
Safari Technology Preview is a standalone browser that lets developers test upcoming WebKit features before they land in the public Safari release. It updates approximately every two weeks and is free to download from Apple’s developer portal.
What This Means
For users, the most immediate benefit is increased security against phishing and a faster, smoother browsing experience. For web developers, the new capabilities—especially threaded animations, customizable selects, and scroll anchoring—reduce the need for workarounds and JavaScript polyfills, enabling more performant and standards-compliant websites.
“This release signals Apple’s commitment to catching up with modern web standards while prioritizing user safety,” concluded the WebKit engineer. “We encourage developers to test their sites immediately.”
Safari Technology Preview 238 is available now. All users on compatible macOS versions are urged to update promptly.