Release Notes for Safari Technology Preview 52

Safari Technology Preview Release 52 is now available for download for macOS Sierra and macOS High Sierra. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab. This release covers WebKit revisions 228856-229535.

Legacy NPAPI Plug-ins

  • Removed support for running legacy NPAPI plug-ins other than Adobe Flash

Service Worker

  • Changed Fetch event release assert to take into account the fetch mode (r228930)
  • Changed to not use a Service Worker in the case of document redirection if it will be already served by AppCache (r229086)
  • Fix loads for a Document controlled by a Service Worker to not use AppCache (r229181)
  • Updated Service Worker to respect IndexedDB and DOM cache partitioning (r229483)


  • Added support for preconnect link headers (r229308)
  • Fixed converting a load to a download to work with async policy delegates (r229177)
  • Prevented DNS prefetching from being re-enabled (r229061)


  • Fixed handling undefined global variables with the same name as an element ID (r229451)
  • Made Number.isInteger an intrinsic (r228968)


  • Added new CSS env() constants for use with fullscreen (r229475)
  • Fixed ::selection CSS stroke-color and stroke-width to be applied to selected text in text fields (r229147)


  • Fixed HTML pattern attribute to set u flag for regular expressions (r229363)
  • Fixed replaceState causing back and forward navigation problems on a page with <base href="/"> (r229375)
  • Fixed to cancel navigation policy check in addition to cancelling the existing provisional load (r228922)


  • Added more accessibility events support (r229310)
  • Dispatched accessiblesetvalue event (r229112)
  • Fixed keyboard focus to follow the VoiceOver cursor into web content or within web content (r228857)
  • Fixed WebKit running spell checker even on non-editable content text (r229500)

Web Driver

  • Fixed clicking on a disabled option element to not produce an error (r229212)
  • Fixed stale elements not getting detected when removed from the DOM (r229210)
  • Fixed failed provisional loads causing “Navigate To” command to hang (r228887)
  • Fixed script evaluations via WebDriver to have a user gesture indicator (r229206)

Web Inspector

  • Changed Canvas Tab to scroll into view and inspect an element if Canvas has a DOM node (r229044)


  • Added cache for memory address and size on an instance (r228966)


  • Fixed the webkitfullscreenchange event to fire at the same time as :-webkit-full-screen pseudo selector changes (r229466, r229487)

Bug Fix

  • Fixed copying a table from the Numbers app and pasting into iCloud Numbers (r229503)