Release Notes for Safari Technology Preview 66

Safari Technology Preview Release 66 is now available for download for macOS Mojave and macOS High Sierra. If you already have Safari Technology Preview installed, you can update in the Software Update pane of System Preferences on macOS Mojave and from the Mac App Store’s Updates tab on macOS High Sierra. After updating to macOS Mojave, you may have to reinstall Safari Technology Preview.

This release covers WebKit revisions 235669-236195.

This release of Safari Technology Preview has a known issue where launching SafariDriver fails.

Web Share API

  • Implemented the Web Share API (r235925)

Conic Gradients

  • Added support for Conic Gradients (r235772)
  • Fixed angle interpretation for Conic Gradients (r235868)
  • Fixed color stop blending in Conic Gradients for stops past the first stop (r235999)


  • Enabled WebRTC Unified Plan as an Experimental Feature (r236144)
  • Exposed RTCRtpSender.setParameters (r235714)
  • Introduced a backend for RTCRtpTransceiver (r235719)

Shadow DOM

  • Fixed :first-child, :last-child, :nth-child, and :nth-of-type to work on shadow root’s children (r235917)
  • Fixed mouseenter and mouseleave events to get dispatched when there is a capturing event listener for a slot ancestor (r235865)


  • Added support for double-position gradient color stop syntax (r236155)

Web Inspector

  • Updated the bezier curve editor for Dark Mode (r235998)
  • Changed to generate CSSKeywordCompletions from backend values (r236091)
  • Fixed imported recordings that are unable to be viewed after navigation (r235937)
  • Fixed opening Web Inspector with a selected element that might immediately scroll that element off screen in the DOM Tree outline (r235996)
  • Changed to record actions performed on ImageBitmapRenderingContext (r236008)
  • Fixed Source View to scroll to show the line when a breakpoint is hit inside of a <script> in an HTML resource (r236028)
  • Fixed a Location popover triggering for a hidden Location column when clicking a row in the Script Events grid of the Timelines tab (r235997)


  • Fixed XMLHttpRequest open() to throw a SYNTAX_ERR exception if the method is empty or the URL cannot be resolved (r235808)
  • Fixed overrideMimeType to not update the Content-Type header in the XMLHttpRequest response (r235844)

Apple Pay

  • Updated to dispatch a paymentmethodchange event when the payment method changes (r235833)
  • Renamed the -apple-pay-button-type value checkout to check-out (r235754)


  • Fixed Symbol.prototype.description to handle a null Symbol (r235712)


  • Added Media Capabilities API as an Experimental Feature (r235675)
  • Added support for HEVC codec types in Media Capabilities (r236094)
  • Fixed track.onmute not getting called for a remote MediaStreamTrack when its counter part track is removed from the peer connection (r236090)
  • Updated to include supported frame rates in video capture presets (r235760)
  • Simplified logic when changing RealtimeMediaSource settings (r235670)
  • Changed the middle value to center in WebVTT for consistency with CSS (r236143)

Web Animations

  • Fixed a failure that occurred when interrupting an accelerated CSS transition on a composited element in-flight (r235843)
  • Fixed accelerated animations to correctly respect positive delay values (r235854, r236072)

Web Assembly

  • Optimized JavaScript to Web Assembly call by removing Vector allocation (r235778)

Password AutoFill

  • Automatically submit login forms when filling credentials with Password AutoFill
  • On MacBook Pro with Touch Bar, require authentication with Touch ID to fill passwords into web pages; this can be changed in Safari’s AutoFill preferences