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Safari Technology Preview 63 Offers Bug Fixes and Feature Improvements

Safari Technology Preview 63 Offers Bug Fixes and Feature Improvements

Apple on Wednesday released Safari Technology Preview 63, which is the latest version of their developer preview web browser, which allows developers and other interested parties to test features that may or may not, debut in future public release versions of Safari.

Release 63

Known Issue

  • Adobe Flash content does not load on macOS Mojave

Dark Mode

  • Fixed the appearance of the Smart Search Field in Dark mode on macOS Mojave


  • Fixed a Safari Technology Preview application crash that could happen when waking one’s Mac from sleep
  • Fixed a Safari Technology Preview application crash that could happen when navigating between web pages

Custom Elements

  • Fixed document.open and document.write to throw errors while the HTML parser is synchronously constructing a custom element
  • Implemented customElements.upgrade()
  • Fixed erroneous garbage collection for properties set on window.customElements
  • Changed innerHTML to not synchronously create a custom element
  • Made HTML parser immediately execute custom elements reactions after synchronously constructing a custom element
  • Fixed the crash that occurs when a custom element reaction callback throws an exception


  • Prevented creating composited layers for renderers unless they are part of the fullscreen subtree
  • Fixed switching tabs to not close the picture-in-picture window

Web Animations

  • Fixed accelerated animations to respect a positive delay value
  • Fixed transitions added immediately after element creation to work as expected
  • Fixed animation stopping with object-fit:contain on an animated 2D canvas


  • Fixed navigator.sendBeacon to work in pagehide event callbacks
  • Fixed setting the table layout to fixed causing incorrect cell width calculations


  • Fixed returning nothing for various previous text marker APIs from one <div> or <p>node to another

Web Inspector

  • Fixed inconsistent background color for the JavaScript Debugger breakpoint editor in Dark Mode
  • Fixed the contrast for the disabled breakpoints banner in Dark Mode
  • Fixed a white background for the Search sidebar panel text field in Dark Mode
  • Fixed the source code text editor thread indicator widget contrast in Dark Mode
  • Included a full URL tooltip when hovering the name in the Network Tab

Internationalization API

  • Changed the Internationalization API to ignore encoding when parsing BCP 47 language tag from an ISO 15897 locale string passed via LANG

WebGL 2

  • Added support for compilation of GLSL ES version 300 shaders


  • Changed to allow href attribute without xlink on SVG elements

Users can either download the update from the Safari Technology Preview website, or if they already have the browser installed, they can download it via 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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