Release Notes for Safari Technology Preview 63

Safari Technology Preview Release 63 is now available for download for macOS High Sierra and the beta of macOS Mojave. If you already have Safari Technology Preview installed, you can update from the Mac App Store’s Updates tab on macOS High Sierra and in the Software Update pane of System Preferences on macOS Mojave. This release covers WebKit revisions 234197-234684.

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 (r234674)
  • Fixed a Safari Technology Preview application crash that could happen when navigating between web pages (234462)

Custom Elements

  • Fixed and document.write to throw errors while the HTML parser is synchronously constructing a custom element (r234680)
  • Implemented customElements.upgrade() (r234507)
  • Fixed erroneous garbage collection for properties set on window.customElements (r234578, r234585)
  • Changed innerHTML to not synchronously create a custom element (r234577)
  • Made HTML parser immediately execute custom elements reactions after synchronously constructing a custom element (r234608)
  • Fixed the crash that occurs when a custom element reaction callback throws an exception (r234539)


  • Prevented creating composited layers for renderers unless they are part of the fullscreen subtree (r234291)
  • Fixed switching tabs to not close the picture-in-picture window (r234264)

Web Animations

  • Fixed accelerated animations to respect a positive delay value (r234279)
  • Fixed transitions added immediately after element creation to work as expected (r234250)
  • Fixed animation stopping with object-fit:contain on an animated 2D canvas (r234343)


  • Fixed navigator.sendBeacon to work in pagehide event callbacks (r234684)
  • Fixed setting the table layout to fixed causing incorrect cell width calculations (r234630)


  • Fixed returning nothing for various previous text marker APIs from one <div> or <p> node to another (r234275)

Web Inspector

  • Fixed inconsistent background color for the JavaScript Debugger breakpoint editor in Dark Mode (r234219)
  • Fixed the contrast for the disabled breakpoints banner in Dark Mode (r234464)
  • Fixed a white background for the Search sidebar panel text field in Dark Mode (r234394)
  • Fixed the source code text editor thread indicator widget contrast in Dark Mode (r234465)
  • Included a full URL tooltip when hovering the name in the Network Tab (r234431)

Internationalization API

  • Changed the Internationalization API to ignore encoding when parsing BCP 47 language tag from an ISO 15897 locale string passed via LANG (r234260)

WebGL 2

  • Added support for compilation of GLSL ES version 300 shaders (r234380)


  • Changed to allow href attribute without xlink on SVG elements (r234683)