Release Notes for Safari Technology Preview 255

Safari Technology Preview Release 255 is now available for download for macOS Golden Gate and macOS Tahoe.

October 22, 2026 12 min readOriginal

Safari Technology Preview Release 255 is now available for download for macOS Golden Gate and macOS Tahoe. If you already have Safari Technology Preview installed, you can update it in System Settings under General → Software Update.

This release includes WebKit changes between: 322011@main…323397@main.

Accessibility

Resolved Issues

Fixed VoiceOver presses dispatching a click event with an event.detail of 0. (322978@main) (187732224)
Fixed radio buttons in a group to be exposed as required when the required attribute is set on one of the buttons. (322894@main) (189100525)
Fixed list box accessibility children not updating when options are added or removed. (323117@main) (189412211)

Animations

Resolved Issues

Fixed getComputedStyle() ignoring the pseudo-element when checking whether a property is being animated. (322681@main) (188502400)
Fixed requestAnimationFrame() handles to use the full unsigned long range defined by the IDL. (322922@main) (189270148)
Fixed view transition setup to flush the update callback queue. (323173@main) (189533643)

CSS

Resolved Issues

Fixed font-family: initial acting like font-family: inherit instead of resolving to the initial value. (322304@main) (54306281)
Fixed box-sizing: content-box being ignored for percentage-height tables (display: table), which caused vertical padding to be dropped. (322812@main) (122587242)
Fixed min-width: max-content being ignored for the min-content contribution of a percentage-width replaced element. (322974@main) (179947068)
Fixed the top color extension to use relative colors with filters when applicable. (323153@main) (186098400)
Fixed Range.getBoundingClientRect() returning empty rects for content inside a content-visibility: hidden subtree. (323204@main) (186165755)
Fixed elements using a background image that depends on currentColor not repainting when the current color changes. (323240@main) (188036420)
Fixed subgrid implicit grid-area line names being matched by the first substring instead of the suffix. (322238@main) (188203288)
Fixed tree-scoped var() and custom function references inside an @function failing to resolve when the function is called from a :host rule. (322679@main) (188206030)
Fixed an issue where duplicate anchor-name values among <model> elements in a spatial portal resolved unpredictably. (322709@main) (188209540)
Fixed @scope so that structural DOM changes correctly invalidate scope membership when the scoping root selector depends on them. (322680@main) (188398757)
Fixed revert inside @starting-style dropping @starting-style declarations from lower cascade layers. (322688@main) (188463947)
Fixed the rotate property to preserve the sign of the axis when serializing. (322682@main) (188493811)
Fixed revert and revert-layer using the wrong cascade origin for visited and unvisited link styles, which wrongly disabled native appearance. (323205@main) (188494505)
Fixed getComputedStyle() serializing the overscroll-behavior shorthand as a single value of the larger axis instead of both axis values. (322685@main) (188534035)
Fixed block-axis multicolumn content being painted at the wrong offset when the column set does not start at the top of the multicol container. (322687@main) (189067503)
Fixed shape-margin values above 65535px on an image shape-outside producing a much smaller float area. (322727@main) (189069223)
Fixed a line-clamp container to establish an independent formatting context. (322767@main) (189090409)
Fixed replaced elements ignoring aspect-ratio when both width and height are auto. (322745@main) (189096923)
Fixed the line-clamp block ellipsis being placed after a <wbr> in a white-space: nowrap line. (322758@main) (189103913)
Fixed an overflowing preserved tab not wrapping to the next line. (322759@main) (189104880)
Fixed the line-clamp block ellipsis not hanging with hanging-punctuation. (322772@main) (189105782)
Fixed text-overflow truncating a unicode-bidi: plaintext line in the wrong direction. (322866@main) (189108555)
Fixed an image shape-outside dropping an above-threshold run that starts in the last column. (322756@main) (189116534)
Fixed line-clamp: auto not being able to clamp between sibling blocks. (322836@main) (189124610)
Fixed line-clamp: auto clamping inside a box with a set height. (322842@main) (189138321)
Fixed the line-clamp block ellipsis being placed on a line that only contains a float. (322791@main) (189151667)
Fixed the baseline of an empty MathML <mpadded> element to account for border-top and padding-top. (322826@main) (189209081)
Fixed CSS grid intrinsic width computation to resolve auto-fill repetitions against the grid container’s minimum and maximum size. (322848@main) (189223527)
Fixed CSS grid column sizing to resolve percentage rows against the block size rather than the inline size when estimating row sizes. (322850@main) (189230010)
Fixed grid container minimum and maximum sizes to respect box-sizing: border-box. (322856@main) (189235347)
Fixed a percentage-width child of a vertical writing mode box to keep following the box’s width after a style change. (322964@main) (189316242)
Fixed cross-fade() to match the CSS Images Level 4 specification and the behavior of other browsers. (322918@main) (189356185)
Fixed grid layout to return the grid’s used block size, so the container’s size is correct once layout is complete. (323053@main) (189357098)
Fixed grid containers to resolve percentage and calc() values for min-width, max-width, min-height and max-height. (323051@main) (189358198)
Fixed :visited style not updating for links inside shadow trees. (323396@main) (189380898)
Fixed baseline alignment of grid items so it is applied after the items have been sized. (323238@main) (189457596)
Fixed attr() to avoid an unnecessary legacy code path in simple cases. (323098@main) (189485680)
Fixed MediaList writes being silently dropped after the owning rule or stylesheet is destroyed. (323203@main) (189496021)
Fixed collapsed SVG shapes and images being painted when visibility: collapse should be treated as hidden. (323110@main) (189496450)
Fixed block boxes after the line-clamp clamp point remaining visible. (323220@main) (189543433)
Fixed content before the line-clamp clamp point losing its lines when it does not change. (323225@main) (189569400)
Fixed block boxes after the line-clamp clamp point still taking up space. (323253@main) (189570948)
Fixed floats after the line-clamp clamp point remaining visible. (323337@main) (189578173)
Fixed adoptedStyleSheets continuing to apply removed sheets after its length is shrunk, and ignoring changes to a sheet after its duplicate is removed. (323233@main) (189579103)
Fixed an implicit @scope rule in a constructed stylesheet adopted by a document matching nothing. (323237@main) (189584948)
Fixed floats making the line-clamp container taller. (323349@main) (189630233)
Fixed floats adding to the scrollable overflow of the line-clamp container. (323353@main) (189641420)
Fixed line-clamp: auto containers having no line clamp until the clamp point is found. (323357@main) (189652879)
Fixed floats painting past the block-end content edge of the line-clamp container. (323390@main) (189653161)
Fixed container size queries truncating fractional container sizes to integers. (323328@main) (189653185)
Fixed absolutely positioned elements whose containing block is an inline after the line-clamp clamp point remaining visible. (323395@main) (189671905)

Editing

Resolved Issues

Fixed DataTransfer treating any format that merely starts with text/plain, such as text/plainfoo, as text/plain. (322954@main) (189265567)

Forms

New Features

Added support for <button> in the native appearance of <select>. (322716@main) (178876621)

Resolved Issues

Fixed :open no longer matching a <select> whose base appearance picker is still showing. (322666@main) (188911581)
Fixed a <select> element computing its selected option’s style from outdated ancestor styles. (322665@main) (189109118)
Fixed a vertical range slider fill overshooting its value when tick marks are present and the thumb is hidden. (322780@main) (189116567)

HTML

Resolved Issues

Fixed a <style> element’s sheet to be built from its child text content instead of descendant text. (322128@main) (188047912)
Fixed tabbing to a popover invoker to move focus to the popover itself when the popover is focusable. (323172@main) (188267440)
Fixed module <script> elements with an empty or invalid src to fire the error event asynchronously instead of synchronously. (323198@main) (189384155)
Fixed setting src to the empty string on a connected <script> element to fire an error event. (323200@main) (189385352)
Fixed <script> elements with an ASCII-whitespace-only src being treated as having an empty src. (323236@main) (189386063)

JavaScript

Resolved Issues

Fixed Object.defineProperty to read descriptor fields after converting the property key, so side effects from key conversion are respected. (322982@main) (179389067)
Fixed an issue where errors thrown by another realm’s built-ins such as Number, String, and Math functions came from the caller’s realm after DFG optimization. (323152@main) (189057417)
Fixed catch parameters named await to be rejected as a syntax error in contexts where await is not an identifier. (322702@main) (189183089)
Fixed await to be treated as an identifier in a non-async function nested in the parameters of an async function. (322703@main) (189183268)
Fixed unary + so it no longer changes the evaluation order of operands in binary expressions. (322817@main) (189267513)
Fixed constant array literal elements to be evaluated only once when emitting bytecode for array literals. (322943@main) (189295197)
Fixed instanceof with a bound function reading the target’s prototype property when the left-hand side is a primitive. (322956@main) (189388195)
Fixed Array.fromAsync to get next from the async iterator before constructing the this value. (322967@main) (189402953)
Fixed using and await using declarations being rejected inside a function nested in a switch case or default clause. (323061@main) (189472811)
Fixed for-in skipping indexed properties of functions. (323086@main) (189504414)

Media

Resolved Issues

Fixed remote audio participants no longer autoplaying on web sites using real-time calls. (323320@main) (182922583)
Fixed WebVTT cue display so the backdrop no longer overflows outside of the cue. (323325@main) (183472002)
Fixed an issue where video using Media Source Extensions never started playing on some sites, such as disneyplus.com. (322877@main) (184182838)
Fixed WebCodecs ignoring the profile, bit depth, and chroma subsampling fields in VP9 codec strings. (322962@main) (188868426)
Fixed the WebCodecs AV1 encoder reporting support for 10-bit, 12-bit, monochrome, and 4:4:4 or 4:2:2 codec strings that it always encodes as 8-bit 4:2:0. (322975@main) (188882755)
Fixed WebCodecs computing incorrect plane layouts for I422 and I444 VideoFrame objects. (322972@main) (188885351)

Networking

Resolved Issues

Fixed failed modulepreload resource loads getting stuck in the cache by retrying them. (323305@main) (124280450)
Fixed a regression where XMLHttpRequest and fetch sent an empty request body for a disk-backed File when the page is controlled by a service worker. (323318@main) (183071407)

Rendering

Resolved Issues

Fixed a block-level box with aspect-ratio inside a float growing when its content changes. (322742@main) (188872195)
Fixed selection gaps not being painted for a line whose selection top is above its block container. (322750@main) (189113277)
Fixed an issue where an element’s box size was incorrect when a padding change was followed by another style change before layout. (322929@main) (189319402)
Fixed an issue where changing a table cell’s width did not resize its row in a table with a vertical writing mode. (322934@main) (189322207)

SVG

New Features

Added support for the side attribute on the SVG <textPath> element. (323115@main) (174710714)
Enabled the inline layout engine for SVG text. (323141@main) (189532515)

Resolved Issues

Fixed zero intrinsic size not being respected for SVG in <object> and <embed> elements. (322529@main) (132152736)
Fixed SVG elements inside hidden containers being focusable. (322650@main) (171590890)
Fixed an issue where changing a list attribute detached the SVGNumber, SVGLength, and SVGPoint objects held by a script instead of updating them. (323046@main) (186835842)
Fixed changing only paint-order not triggering a repaint of SVG content. (322013@main) (188533466)
Fixed SVG animations continuing to run when the animation element or an ancestor fails conditional processing. (322829@main) (188780260)
Fixed svgView() fragments with an invalid or zero-size viewBox drawing the SVG unscaled. (323217@main) (189611839)

Security

Resolved Issues

Fixed external scripts blocked by the strict-dynamic Content Security Policy keyword to fire an error event. (323191@main) (189386852)

Web API

New Features

Added support for the cross-origin-isolated Permissions Policy feature. (322663@main) (189124490)
Added support for transferring streams to an AudioWorklet. (323327@main) (189677199)

Known Issues

document.activeElement returns the <html> element instead of null for HTML documents with no body, which differs from other browsers and breaks the WebDriver Get Active Element command. (323385@main) (190343977)

Resolved Issues

Fixed an issue where interactive-widget=resizes-content did not reflect the correct innerHeight, causing the sign-in screen on kidshibbett.com to disappear from view. (186817825)
Fixed pointermove firing on the parent of a pointerover target that is removed during pointerover. (322451@main) (188882772)
Fixed Cross-Origin-Embedder-Policy not being ignored in non-secure contexts. (322838@main) (189193030)
Fixed Range.deleteContents() and Range.extractContents() removing nodes outside the range when the range end is moved during the operation. (322920@main) (189262302)
Fixed the element.dataset named getter to no longer match non-data-* attributes or invalid property names. (322936@main) (189263319)
Fixed NodeIterator leaving its reference on a detached node when an ancestor of the reference node with no following node in the root is removed. (322933@main) (189263890)
Fixed requestIdleCallback() handles above 2^31 so they can be cancelled with cancelIdleCallback(). (322942@main) (189266546)
Fixed secure context status being determined after document creation instead of when the document is created. (322939@main) (189268799)
Fixed the document’s default event handler running twice for bubbling events targeted at the document, which fired DOMActivate twice. (323065@main) (189379133)
Fixed requestIdleCallback callbacks no longer running after removing a same-origin iframe that had a pending setTimeout. (323148@main) (189379748)
Fixed Window-only and DedicatedWorkerGlobalScope-only types being deserialized in other kinds of workers. (323120@main) (189423491)
Fixed moveBefore() leaving selectors that depend on the child list, such as :has() and :empty, stale after a move. (323044@main) (189461850)
Fixed FileSystemHandle objects being deserialized in non-secure contexts. (323219@main) (189588333)
Fixed SpeechRecognitionResultList being exposed in non-secure contexts. (323326@main) (189631080)
Fixed DOMException and QuotaExceededError not being exposed in every global scope. (323313@main) (189677643)

Deprecations

Removed the unimplemented document.implementation.createCSSStyleSheet() method. (322805@main) (142045904)

Web Extensions

New Features

Added support for browser.notifications.update() in web extensions. (322071@main) (187615870)
Added support for browser.notifications.clear(), browser.notifications.getAll(), and browser.notifications.getPermissionLevel() in web extensions. (322297@main) (187616262)

Resolved Issues

Fixed storage.local.get() returning the same array or object instance for distinct empty arrays and objects in a stored value. (323003@main) (189204323)
Fixed extension page subframes to have unpartitioned storage access. (323034@main) (189301936)

Web Inspector

New Features

Added a CSS keyframe animation editor to Web Inspector. (322820@main) (15801500)
Added stack trace popovers to Web Inspector. (322748@main) (20582649)
Added evaluation previews to the Web Inspector console. (322754@main) (182773473)
Added basic WGSL syntax highlighting. (322649@main) (189147091)
Added Web Inspector Graphics instrumentation for updates to the label of WebGPU devices and pipelines. (322793@main) (189247758)

Resolved Issues

Fixed Find in the Elements tab not matching HTML elements and attributes when the search text contains a space character. (323277@main) (109289803)
Fixed Log Message breakpoint actions to log objects as rich console arguments instead of plain text. (322733@main) (116907593)
Fixed the Infos and Debugs scope bar items disappearing from the console after the console is cleared. (323269@main) (125621103)
Fixed await not being supported in the console in some scenarios. (323272@main) (127381329)
Fixed Styles to correctly account for declarations marked !important within a CSS @layer rule when computing style overrides. (323275@main) (151931708)
Fixed console log messages dismissing the DOM Event popover. (323306@main) (153842239)
Fixed Beacon resources in the Sources tab showing an error instead of the response content. (323270@main) (170805067)
Fixed the wrong source code location being shown for inline scripts with a source map. (322747@main) (182487329)
Fixed Web Inspector to compare resolved resource types after receiving a response. (323274@main) (183988946)
Fixed Web Inspector to no longer automatically invoke native getters on functions and prototype objects. (323271@main) (184191697)
Fixed the Web Inspector frame selector popup disappearing when paused in the debugger. (322739@main) (186908754)
Fixed Web Inspector to clear the active call frame when its target is removed. (322734@main) (186984661)
Fixed Web Inspector not offering JavaScript runtime completions for BigInt values. (322731@main) (186985019)
Fixed Web Inspector to preserve explicit execution context selections across back-forward navigation. (323281@main) (186985083)
Fixed Web Inspector to preserve newer execution context selections during navigation. (323282@main) (186985387)
Fixed the Network emulation tab bar icon appearing inverted in dark mode in Web Inspector. (322729@main) (187758172)
Fixed the Styles panel showing var() with a non-ASCII custom property name, such as var(--色), as invalid even though it resolves. (322076@main) (188169850)
Fixed the debugger leaving no active call frame when the active target resumes while another target is still paused. (322843@main) (188827760)
Fixed Web Inspector to only update the currently active Timeline recording. (322738@main) (189207884)
Fixed the Elements tab to include the host element when pushing a pseudo element. (322871@main) (189321868)
Fixed Web Inspector to complete rendering notifications before the next rendering update. (322873@main) (189322496)
Fixed back/forward cache restore incorrectly reporting a navigation failure after a pagehide beacon. (322983@main) (189350210)
Fixed Web Inspector reporting “domain already enabled” errors when going back to a page restored from the back/forward cache after a process swap. (323239@main) (189375630)
Fixed the loaderId changing when a navigation continues in another process. (323167@main) (189567072)
Fixed the selected node not being highlighted when hovering keyframe headers in the Elements tab. (323260@main) (189669693)
Fixed the Elements tab offering Duplicate Selector, Add Rule, and Create Rule context menu actions for keyframes. (323263@main) (189669755)
Fixed filtering styles in the Elements tab incorrectly hiding matching keyframe sections. (323262@main) (189669803)
Fixed the Network tab reported response timing not accounting for network throttling. (323261@main) (189669852)
Fixed the Storage tab hiding or mishandling entries with an empty key or value. (323267@main) (189669876)
Fixed importing a Timeline recording modifying more than the imported recording. (323268@main) (189670026)
Fixed search results missing matches on consecutive lines. (323264@main) (189670067)
Fixed revealing a source location from the Console selecting the wrong location in a pretty printed script. (323265@main) (189670127)
Fixed the Console missing known parameters for some native DOM methods. (323307@main) (189689587)
Fixed an uncaught ReferenceError for row in the Layout Timeline overview graph. (323308@main) (189689709)
Fixed an uncaught TypeError in the Console when formatting table parameters for a logged message with no parameters. (323363@main) (189724207)

WebGL

Resolved Issues

Fixed WebGL default framebuffer queries to be answered at the WebGLRenderingContext level. (322700@main) (188899947)
Fixed an issue where resizing a canvas with separate width and height assignments could lose the WebGL context. (323298@main) (188900757)
Fixed a WebGL canvas becoming blank after its drawing buffer was resized when painted without accelerated compositing on Windows. (322870@main) (189321624)
Fixed full clears of renderbuffers being treated as partial clears under robust resource initialization. (323300@main) (189506198)
Fixed renderbuffers being initialized on the CPU in the Metal backend. (323297@main) (189606864)