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Safari Technology Preview 66 Brings The Ever-Popular Bug Fixes and Feature Improvements

Safari Technology Preview 66 Brings The Ever-Popular Bug Fixes and Feature Improvements

Apple on Wednesday released Safari Technology Preview 66, the latest version of their developer preview web browser. The preview version of the popular browser allows developers and other interested users to try out features that may or may not, debut in future public release versions of Safari.

Release 66

Web Share API

  • Implemented the Web Share API

Conic Gradients

  • Added support for Conic Gradients
  • Fixed angle interpretation for Conic Gradients
  • Fixed color stop blending in Conic Gradients for stops past the first stop


  • Enabled WebRTC Unified Plan as an Experimental Feature
  • Exposed RTCRtpSender.setParameters
  • Introduced a backend for RTCRtpTransceiver

Shadow DOM

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


  • Added support for double-position gradient color stop syntax

Web Inspector

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


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

Apple Pay

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


  • Fixed Symbol.prototype.description to handle a null Symbol


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

Web Animations

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

Web Assembly

  • Optimized JavaScript to Web Assembly call by removing Vector allocation

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

The update can be downloaded from the Safari Technology Preview website, or if the browser is already installed, it can be updated via the “Update” tab in the Mac App Store. Full release notes for the update are available on the same website.

While the preview is intended for use by developers and advanced users, in order to provide Apple with feedback on the development of the Safari browser, it can be run side-by-side with the release version of Safari. The app doesn’t require a developer account to download and install. For more information, visit the Safari Technology Preview website.

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