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Apple Releases Safari Technology Preview 138 Release Offers Bug Fixes and Performance Improvements

Apple Releases Safari Technology Preview 138 Release Offers Bug Fixes and Performance Improvements

Apple on Thursday released Safari Technology Preview 138, the latest version of their developer preview web browser. The preview version of Apple’s popular browser offers developers and other interested users the ability to try out features that may or may not, debut in future public release versions of Safari.

Safari Technology Preview‌ release 138 includes bug fixes and performance improvements for Web Inspector, CSS, JavaScript, WebAssembly, Experimental Model Element, Accessibility, Web API, Content Security Policy, Media, Apple Pay, and Web Extensions.

‌Safari Technology Preview‌ release 138 is built on the new Safari 15.4 update included in macOS Monterey, and as such, it includes several Safari 15 features.

The preview is available for both macOS Monterey and macOS Big Sur.

Release 138

Web Inspector

  • Elements Tab
    • Added support for Cascade Layers in the Styles sidebar (r286558)
    • Added a swatch for align-items and align-self (r286875)
    • Added a swatch for justify-contentjustify-items, and justify-self (r286885)
    • Added CSS variable names to property name completion list (r286890)
    • Added an option to group CSS variables by value type in the Computed sidebar (r286876)
    • Enabled fuzzy matching for CSS completions in the Styles sidebar (r286792r286611)


  • Enabled :focus-visible pseudo-class by default (r286783r286776r286775)
  • Enabled the resolution media query by default (r286874)
  • Enabled the CSS Contain property by default (r286828)
  • Changed to account for captions when flexing tables with specified sizes (r286593)
  • Fixed perspective() less than or equal to 1px to be clamped to 1px (r286591)
  • Fixed gap to work correctly when flex-direction: column-reverse is applied (r286654)
  • Fixed the serialization of CSSImportRule (r286668)
  • Unprefixed -webkit-mask (r286795)
  • Unprefixed CSS value text-align: -webkit-match-parent (r286803)
  • Updated color-mix() to support srgb-linear and alpha premultiplication (r286568)

Experimental Model Element

  • Added load and error events to distinguish resource load from model readiness (r286836)


  • Fixed various issues with complicated rendering of VTT cues (r286743)

Web Animations

  • Added a way to run scripted animations via CustomEffect (r286555)
  • Exposed a frameRate property to Web Animations (r286915)


  • Improved WebAuthn Level 2 standards compliance by supporting the displayName (r286746)


  • Fixed transform-origin on SVG elements to take into account the transform reference box origin (r286942)


  • Changed to group radio buttons with no form owner (r286855)
  • Fixed the range of <input type=”time”> to be reversible (r286581)
  • Fixed an <input> that’s been autofilled with obscured content to still be editable (r286814)
  • Implemented AbortSignal.throwIfAborted (r286904)
  • Improved <input type=”datetime-local”> value parsing and sanitization (r286869)
  • Restored navigator.hardwareConcurrency (r286550)
  • Fixed setting onselectionchange content attribute to add an event listener (r286898)

Service Workers

  • Enabled NavigationPreloadManager by default (r286540)
  • Added support for ServiceWorker downloads (r286944)
  • Fixed “no-cache” network error (r286655)
  • Fixed same-site lax cookies not sent by fetch event handler after page reload (r286656)


  • Closed WebRTC allocation sequence shared socket in case of sequence network failure (r286539)


  • Added preparation of WebAssembly.Memory imports in Wasm/ESM modules (r286703)

Web Extensions

  • Added support for changed web_accessible_resources declaration with manifest_version 3
  • Fixed runtime.onMessage listeners not supporting Promise returns for the reply message
  • Show error messages for incorrect match patterns in web_accessible_resources
  • Show error message to devtools tabs in Web Inspector when inspecting unsupported targets
  • Show error message when the service worker background script fails to load

Bug Fixes

  • Fixed an issue introduced in Safari Technology Preview 137 where pop-up windows wouldn’t open

While the preview is intended for use by developers and advanced users, in order to provide Apple with feedback on the development of the Safari browser, it can be run side-by-side with the release version of Safari. The app doesn’t require a developer account to download and install. For more information, visit the Safari Technology Preview website.