Safari 26.3 brings welcome improvements for users and developers

Alongside today's system updates, Apple has released Safari 26.3, with a mix of under-the-hood improvements and at least one major usability upgrade for Vision Pro users. Here are the details.

Better fullscreen handling on visionOS, efficiency improvements for all

With Safari 26.3, Vision Pro users on visionOS 26.3 will see Safari automatically dim their surroundings when a video enters fullscreen, a change Apple says helps "put the focus on the content."

In addition, Safari 26.3 introduces support for Zstandard (Zstd), an open, real-time compression algorithm developed by Meta that essentially compresses text-based web assets before they're delivered to browsers and then decompresses them quickly on-device. Apple says that "Zstandard decompresses quickly, reducing the workload on users' devices. It also compresses fast enough to do on-the-fly, whereas Brotli is typically pre-compressed during your build process."

Apple notes that users need to be running Safari 26.3 on iOS 26.3, iPadOS 26.3, visionOS 26.3, and macOS Tahoe 26.3 for Zstd support to work.

Developer improvements in Safari 26.3

If you're a developer, you might be happy to know that Safari 26.3's Navigation API now "exposes a AbortSignal on NavigateEvent which triggers when the navigation is aborted," which Apple says is a "reliable way to cancel ongoing work when a navigation gets interrupted."

Finally, WebKit for Safari 26.3 contains the following developer-facing bug fixes and improvements:

CSS

• Fixed a style resolution loop that occurred when a position-try box was inside a display: none ancestor. (163691885)
• Fixed an issue where anchor-positioned elements repeatedly transitioning from display: block to display: none cause position jumps during animation. (163862003)
• Fixed an issue where fixed-positioned boxes using position-area were incorrectly included in the scrollable containing block calculation. (164017310)
• Fixed an issue where text-decoration: underline was rendered too high when text-box-trim was applied to the root inline box. (165945326)
• Fixed a multi-column layout issue where the widows and text-indent properties are applied cause an incorrect indent on the portion of the paragraph that flows into the next column. (165945497)
• Fixed an issue where CSS cursors like move, all-scroll, ew-resize, and ns-resize did not display correctly. (166731882)

DOM

• Fixed incorrect timestamp handling and switched to use the raw touch timestamp. (164262652)

Media

• Fixed an issue where the fullscreen button in visionOS inline video controls did not visually indicate interactivity by extending the glow effect to all button.circular elements. (164259201)
• Fixed Video Viewer mode for iframe videos on macOS. (164484608)
• Fixed an issue where Safari could not play live videos when the sourceBuffer content is removed and re-added causing the seek to not complete. (165628836)

Rendering

• Fixed an issue where positioned or transformed <img> elements containing HDR JPEGs with gain maps would incorrectly render as SDR. (163517157)

Safe Browsing

• Fixed a bug where if Safe Browsing queried for an entry on the Public Suffix List, and a Safe Browsing vendor responded that the whole effective TLD was unsafe, the whole site would be marked as unsafe. (168155375)

To learn more about Safari 26.3, follow this link.

What this means for developers and users

The addition of Zstandard compression is particularly noteworthy as it represents Apple's continued investment in web performance optimization. By supporting real-time compression that doesn't require pre-processing, developers can potentially reduce bandwidth usage and improve load times without changing their build processes. This is especially valuable for dynamic content and applications that generate content on the fly.

For Vision Pro users, the automatic dimming feature when entering fullscreen video mode shows Apple's attention to the unique needs of spatial computing. The immersive nature of Vision Pro means that environmental distractions can significantly impact the viewing experience, and this subtle enhancement helps maintain focus on the content.

The Navigation API improvements with AbortSignal support give developers more robust tools for handling interrupted navigations, which is particularly useful for single-page applications and complex web apps where navigation can be interrupted by user actions or network conditions.

The extensive list of CSS and rendering bug fixes demonstrates Apple's commitment to web standards compliance and visual fidelity. Issues like the HDR JPEG rendering bug and the CSS cursor display problems could have been frustrating pain points for developers, and their resolution should lead to more consistent experiences across browsers.

The Safe Browsing fix is also important for security-conscious users and developers, ensuring that the entire site isn't incorrectly flagged as unsafe when only a specific domain component poses a risk.

Overall, Safari 26.3 represents a solid update that balances user experience improvements with developer tooling enhancements, continuing Apple's pattern of iterative but meaningful browser updates.