Release Notes for Safari Technology Preview 25

Safari Technology Preview Release 25 is now available for download for macOS 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 212356-213542.

Resource Timing

  • Added Resource Timing as an experimental feature enabled by default (r212945)
  • Added Resource Timing support in Workers (r212449)
  • Improved gathering timing information with reliable responseEnd time (r212993)
  • Changed loads initiated by media elements to set the initiatorType to their element name (r212994)

User Timing

  • Enabled User Timing by default as an experimental feature (r212945)
  • Changed performance.measure in Workers to throw a SyntaxError if provided mark name is not found (r212806)


  • Added support for AES-CFB (r212736)


  • Added a new webglcontextchanged event that is dispatched when the GraphicsContext3D notices that the active GPU has changed (r212637)
  • Changed the onbeforeunload event return value coercion to match specification behavior (r212625)
  • Exposed Symbol.toPrimitive and Symbol.valueOf on Location instances (r212378)
  • Fixed <input type=color> and <input type=range readonly> to prevent applying the readonly attribute to match specifications (r212617, r212610)
  • Fixed handling of <input>.labels when the input type changes from "text" to "hidden" to "checkbox" (r212522)
  • Prevented aggressive throttling of DOM timers until they’ve reached their maximum nesting level (r212845)

Web Inspector

  • Enabled import() for modules in Web Inspector console (r212438)
  • Changed the zoom level in the Settings tab to use localized formatting (r212578)
  • Changed Web Inspector to use the Resources tab when showing files instead of the Network tab (r212761)
  • Changed the split console to be allowed in the Elements, Resources, Debugger, and Storage tabs when Web Inspector is docked to the bottom (r212400)
  • Changed CSS variable uses that are unresolved to get marked with a warning icon (r213187)
  • Fixed the Zoom level user interface to match the the setting value (r212580)
  • Prevented dismissing popovers when dragging a Web Inspector window (r212427)
  • Improved copy and paste behavior for request headers (r212423)
  • Included additional detail in the display name of Timeline data elements (r212570)


  • Fixed centering text inside a button set to display:flex with justify-content:center (r213173)
  • Unprefixed -webkit-line-break (r213094)


  • Prevented fixed elements from bouncing when scrolling beyond the bottom of the page (r212559)
  • Improved text wrapping consistency where text might wrap when its preferred logical width is used for sizing the containing block (r213008)


  • Fixed local audio-only streams to trigger playback to begin (r212696)

Bug Fixes

  • Changed pending scripts to execute asynchronously after stylesheet loads are completed (r212614)
  • Fixed an issue where font-weight in @font-face can cause a font to be downloaded even when it’s not used (r212513)
  • Made special URLs without a host invalid (r212470)