Release Notes for Safari Technology Preview 128

Safari Technology Preview Release 128 is now available for download for macOS Big Sur and betas of 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 278571-279264.

Note: Tab Groups do not sync in this release.

Web Inspector

  • Elements Tab
    • Unused inherited CSS variables are now hidden by default in the Styles panel (r278607)
    • CSS variable names are no longer converted to all lowercase in the Computed panel (r278848)


  • Added support for 12 CSS list-style-type values along with other list style fixes (r279165)
  • Fixed CSSOM “set a CSS declaration” for logical properties (r279044)
  • Fixed new snap containers always snapping to the first scroll position (r278862)
  • Fixed Scroll snap offsets interpreted as scroll positions in a scrollable area (r278868)
  • Fixed flex items staying invisible after initial layout (r278659)
  • Fixed text-decoration: underline not applied to web component (r278602)
  • Stopped computing the min or max sizes of flex items twice (r278865)


  • Ignored Intl.NumberFormat feature options when linked-ICU is old (r278697)
  • Optimized JSON.parse with small data by changing Identifier pool mechanism (r278971)
  • Optimized valueOf call via ToPrimitive (r279053)
  • Fixed that Window should behave like a legacy platform object without indexed setter (r278585)

Live Text

  • Added a mechanism to regenerate text in an image element when it changes dimensions (r278747)
  • Changed mouse events to trigger text recognition only if the cursor is moving (r279059)
  • Text selection inside image elements should not be cleared upon resize (r278775)


  • Reworked handling buffer full in SourceBuffer (r278603)

Performance API

  • Implemented performance.timeOrigin (r278665)


  • Adjusted fetch port blocking for ports 990, 989 (r279099)
  • Fixed Document’s execCommand() and queryCommand() to throw an exception on non-HTML or non-XHTML documents ** (r278974)
  • Fixed EventSource.constructor to not throw an exception when the URL parameter is an empty string (r278763)
  • Implemented width and height attributes on source elements of <picture> (r279108)
  • Improved specification compatibility for the outerHTML setter (r278821)