Release Notes for Safari Technology Preview 155

Safari Technology Preview Release 155 is now available for download for macOS Monterey 12.3 or later and macOS Ventura beta. If you already have Safari Technology Preview installed, you can update in the Software Update pane of System Preferences on macOS Monterey, or System Settings under General → Software Update on macOS Ventura.

This release includes WebKit changes between: 254352@main…254623@main

Note: Shared Tab Groups and syncing for Tab Groups, Website Settings, and Web Extensions are not enabled in this release.

Web Inspector

  • Sources Tab
    • Changed URL breakpoints to also pause when an HTML attribute is set that triggers a load (254488@main)


  • Changed animation-* declarations in @keyframes to be a parse error (254468@main)
  • Enabled new perspective: 0 behavior of clamping to 1 (254420@main)
  • Fixed forced breaks in layout containment (254432@main)
  • Fixed contain: content on the body breaking scrolling (254506@main)
  • Fixed ::placeholder to not support writing-mode, direction, and text-orientation (254416@main)
  • Removed CSS display and float quirks on table and table cell elements (254475@main)


  • Fixed inline box decoration position when the content box is vertically shifted with text-underline-position: under in a vertical writing mode (254554@main, 254593@main)
  • Updated transforms on SVG shapes and groups when the root element size is changed (254538@main)
  • Stopped ignoring nowrap for table cells with nowrap="nowrap" and absolute widths (254505@main)


  • Disabled ShadowRealm for now (the --useShadowRealm flag can enable it) (254483@main)
  • Implemented Temporal.PlainDate[Time].{equals, add, subtract} (Behind the --useTemporal flag) (254366@main)
  • Implemented with and round methods for TemporalPlainDate[Time] (Behind the --useTemporal flag) (254565@main)
  • Optimized eval call in DFG / FTL compilers (254367@main)


  • Added support for WebVTT-based extended audio descriptions (254502@main)
  • Changed to round the SourceBuffer removal range (254472@main)
  • Fixed incorrect fullscreen video frame in some cases (254462@main)

Scroll to Text Fragment

  • Fixed Scroll To Text Fragment indicator to not show through popup layers (254494@main)
  • Fixed Scroll To Text Fragments to always be scrolled to the center of the frame (254477@main)
  • Fixed maintaining the Scroll to the Text Fragment until a user scroll happens (254403@main, 254507@main)
  • Fixed nodes with display: none to be considered invisible to search (254498@main)


  • Enabled the Reporting API by default (254520@main)
  • Implemented nested Dedicated Workers (254597@main)
  • Implemented no-quirks mode for media, plugin, and UA-inline documents (254526@main)
  • Added support for Cross-Origin-EmbedderPolicy (COEP) violation reporting (254466@main)
  • Added support for PermissionStatus.onchange in workers (254490@main)
  • Fixed the screen size of fullscreen video based on the aspect ratio (254528@main)
  • Fixed erroneous forgiving selectors to not be reported as supported with CSS.supports("selector(...)") (254489@main)
  • Fixed parsing of negative age values in CORS prefetch responses (254410@main)
  • Fixed handling text documents to comply with modern HTML specs (254389@main)
  • Incorrect image srcset candidate chosen for <img> cloned from <template> (254361@main)
  • Fixed lazy-loaded images sometimes not loading (254471@main)
  • Fixed navigating a cross-origin iframe to the same URL to not replace the current HistoryItem (254563@main)
  • Fixed element.removeAttribute("style") to not cause a style-src CSP violation message (254409@main)
  • Fixed text selection on flex and grid box items (254602@main)
  • Fixed wheel events to not stop macOS smooth keyboard scroll (254561@main)


  • Disallowed redirecting to data: or about: URLs (254619@main)


  • Fixed automation session terminating during navigation process swap (254386@main)