Release Notes for Safari Technology Preview 138

Safari Technology Preview Release 138 is now available for download for macOS Big Sur and macOS Monterey. If you already have Safari Technology Preview installed, you can update in the Software Update pane of System Preferences on macOS.

This release covers WebKit revisions 286534-286944.

Note: Tab Groups do not sync in this release.

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-content, justify-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 (r286792, r286611)


  • Enabled :focus-visible pseudo-class by default (r286783, r286776, r286775)
  • 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