Release Notes for Safari Technology Preview 136

Safari Technology Preview Release 136 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 285101-285788.

Note: Tab Groups do not sync in this release.


  • Added support for contain: paint (r285583)
  • Added support for the revert-layer value (r285624)
  • Added flex-basis: content support (r285709)
  • Fixed ::slotted element style to invalidate correctly in nested case (r285211)
  • Fixed ::slotted to not match an active <slot> (r285209)
  • Fixed :host::part(foo) selector to select elements inside shadow roots (r285262)
  • Fixed a mask or isolation to set transform-style to flat (r285482)
  • Fixed border-radius inline style to serialize with valid syntax (r285235)
  • Fixed font-synthesis inline and computed style to be in canonical order (r285383, r285384)
  • Fixed rendering bug with height: min-content, position: absolute, and box-sizing: border-box (r285495)
  • Fixed the default computed value for content to be none for ::before and ::after (r285621)
  • Implemented parsing and animation support for offset-path (r285343)
  • Implemented Scroll To Text Fragment directive parsing (r285528)
  • Implemented transform: perspective(none) (r285255)
  • Removed non-standard -webkit-border-fit CSS property (r285615)
  • Updated the content-size grid width before laying out a grid item with block constraints and aspect-ratio (r285497)

GPU Process

  • Fixed enabling “media source inline painting” by default to work when using GPU Process for media (r285410)


  • Implemented IntlNumberFormat v3 (formatRangeToParts is not implemented yet) (r285418)
  • Implemented Temporal.Instant (r285178)


  • Implemented custom element definition’s disable shadow flag (r285740)
  • Fixed the cssText property for a computed style to return an empty string (r285604)


  • Fixed showing languages and subtitles tracks button and menu for <audio> (r285216)

Web Animations

  • Added support for composite operations for software animations (r285397)
  • Fixed accelerated animations with a single keyframe not accounting for prior forward-filling animations (r285728)
  • Fixed discrete animation of content property not working (r285423)
  • Improved additivity support when animating the transform property (r285631)


  • Implemented add_virtual_authenticator and remove_virtual_authenticator for WebDriver (r285267)

Private Click Measurement

  • Fixed occasionally dropped attribution reports for Private Click Measurement (r285170)

Web Extensions

  • Added support for manifest_version 3 and service_worker background scripts, while also supporting the option of using non-persistent background pages
  • Added support for script and style injection via the browser.scripting APIs
  • Added support for dynamic and session rules via the browser.declarativeNetRequest APIs
  • Fixed an issue with new tab pages not being remembered when switching from Favorites
  • Fixed an issue with long extension descriptions causing the title to be cut-off in Preferences
  • Enforces limits on the size and number of items in extension sync storage

Other Bugs

  • Fixed opening local HTML files when the Develop menu was enabled (r285130)
  • Stopped using a timer to dispatch the source element’s error event asynchronously (r285413)