Apple has released its updated Safari Technology Preview 33 for macOS Sierra and High Sierra today. The preview browser is specifically designed for developers to get an upcoming look at the new web technologies that macOS and iOS will eventually receive.

As with all of the Safari Technology Preview releases, today’s update focuses on changes that directly impact developers and the work they do. Preview 33 includes a long list of updates that address performance, bug fixes, JavaScript, WebRTC, Media Streams and Capture, media, CSS Grid, Web API, Rendering, and Web Inspector.

Developers interested in downloading the latest Safari Technology Preview can do so at Apple’s Safari developer page. Developers already on the latest release can download the update from the Mac App Store.

Here are the full release notes for Safari Technology Preview 33:


  • Fixed an issue that could lead to large memory use in the Safari Technology Preview and web content processes when certain Safari Extensions are installed


  • Fixed for-in optimization static analysis in the bytecode generator (r217438)
  • Improved performance of String.prototype.concat (r217648)
  • Improved the bytecode and type information provided for toLength (r217530)
  • Optimized Map and Set constructors (r217525)


Media Streams and Capture

  • Fixed getUserMedia prompting too often (r217910)
  • Prevented getUserMedia requests from background tabs unless the tab is already capturing (r217930)
  • Prevented getUserMedia from prompting again if the user denied access (r217945)


  • Enabled clients to specify a list of codecs that should require hardware decode support (r217799)
  • Exempted exclusively wall-powered devices from client-required hardware codec support (r217906)
  • Aligned Web Audio implementation to specifications when clients pass a value of 0 for bufferSize to the createScriptProcessor() method (r217919)

CSS Grid

  • Added support for orthogonally positioned grid items (r217486)
  • Fixed the behavior of positioned items without specific dimensions (r217411)
  • Fixed the logical margin applied in the tracks sizing algorithm of auto tracks (r217709)
  • Fixed margin applied when stretching an orthogonal item in a fixed size track (r217705)


  • Aligned <col span> and <colgroup span> limits with the latest HTML specification (r217907)
  • Fixed null content-type and content-length when fetching Blob URLs with XHR (r217901)
  • Fixed getComputedStyle() to return pixel values for left, right, top, and bottom, matching the specifications (r217522)
  • Implemented fromFloat32Array, fromFloat64Array, toFloat32Array, and toFloat64Array for DOMMatrix (r217764)
  • Implemented DOMPointReadOnly.matrixTransform() (r217763)
  • Enabled script modules to be imported via data URLs (r217760)
  • Updated to slightly stricter rules for custom element names from the recent draft standards (r217864)
  • Used the parent box style to adjust RenderStyle for alignment (r217536)
  • Added conditional support for media preloading and aligned media as values (r217863)
  • Aligned preload implementation to specifications with mandatory as value and other alignments (r217962)


  • Changed behavior to remove backing store for layers that are outside the viewport (r217696)
  • Fixed an issue where a frame’s composited content is visible when the frame has visibility:hidden (r217472)
  • Changed behavior to destroy the associated renderer subtree when display:contentsnode is deleted (r217794)

Web Inspector

  • Added contextual menu item to log a WebSocket object to the console (r217912)
  • Added Debug view to the Settings tab for debug settings and experimental features (r217625)
  • Added the ability for the user to choose stylesheet when creating new rules (r217911)
  • Changed the Node Details Sidebar to allow editable key and values in the Attributes table (r217744)
  • Prevented unnecessary layout triggered when a Sidebar is resized while collapsed (r217452)
  • Fixed performing search on reload for an existing query in the Search tab (r217733)
  • Fixed images dragged from Web Inspector to Desktop being named “Unknown.png” (r217584)
  • Fixed an issue where reloading the page after switching from the Resource tab switches back (r217505)
  • Fixed the CodeMirror instance in the ConsolePrompt getting refreshed each time it is shown (r217746)
  • Fixed showing active Web Sockets when opening Web Inspector (r217721)
  • Fixed an issue preventing the go-to arrow to inspect Web Sockets that receive >50 messages per second (r217690)
  • Improved the reliability of automatically pausing in auto-attach when inspecting a JSContext (r217509)

Bug Fixes

  • Enabled AirPods to work with Netflix (r217858)
  • Fixed stuttering audio in YouTube when the page changes visibility (r217936)

Check out 9to5Mac on YouTube!

FTC: We use income earning auto affiliate links. More.

Check out 9to5Mac on YouTube for more Apple news:

You’re reading 9to5Mac — experts who break news about Apple and its surrounding ecosystem, day after day. Be sure to check out our homepage for all the latest news, and follow 9to5Mac on Twitter, Facebook, and LinkedIn to stay in the loop. Don’t know where to start? Check out our exclusive stories, reviews, how-tos, and subscribe to our YouTube channel

About the Author