This article provides information about the changes in Firefox 122 that affect developers. Firefox 122 was released onJanuary 23, 2024.

Changes for web developers

HTML

• <hr> elements are now allowed as children of<select> elements. This is a new feature that improves the readability of select lists with many options. (Firefox bug 1830909).
• Thetype HTML attribute no longer has an effect if set tonone,disc,circle orsquare in<ol> and no longer has an effect if set to1,a,A,i orI in<ul>. Astype is a deprecated attribute for<ul> and<ol> lists, these should be styled withlist-style-type CSS property instead. (Firefox bug 1868087).

CSS

• The CSSoffset-position property is now available by default. It defines the initial position of an element on a path. (Firefox bug 1598152)

• The various methods for defining a CSSoffset-path — including<basic-shape>,<coord-box>, andurl() — are now enabled by default. (Firefox bug 1598159)

• The CSSray() function is now available by default. You can use this function to define anoffset-path as a line segment that begins from anoffset-position and extends in the direction of the specified angle. (Firefox bug 1598151)

• Theclip-path andoffset-path properties now acceptrect() andxywh() shape functions. These<basic-shape> values allow the clipping and offsetting of elements with a rectangle defined by distance from the edge of the element (rect()) or coordinates and size (xywh()). (Firefox bug 1868722).

JavaScript

• TheArrayBuffer.prototype.transfer() andArrayBuffer.prototype.transferToFixedLength() methods can now be used totransfer ownership of memory from oneArrayBuffer to another. After transfer, the original buffer is detached from its original memory and hence unusable; the state can be checked usingArrayBuffer.prototype.detached. (SeeFirefox bug 1865103 for more details.)

• For parity with other browsers,Date.parse() and theDate() constructor only consider the first three letters of the specified month whennon-standard date strings are parsed. Previously only truncated values of the full month name with three or more characters were accepted (SeeFirefox bug 1862910 for more details.)

SVG

Removals

• Removed support fordata: URLs in SVG<use> elements and via theSVGUseElement interface to preventXSS attacks.The legacy functionality may be re-enabled by setting thesvg.use-element.data-url-href.allowed preference totrue, although this is not recommended for security reasons (Firefox bug 1806964).

APIs

• TheLargestContentfulPaint API is now supported.This API is part of thePerformance APIs and provides timing information about the largest image or text paint before users interact with a web page (Firefox bug 1866266).

DOM

• TheHTMLSelectElement.showPicker() method is now supported, allowing the browser picker for a<select> element to be programmatically launched when triggered by user interaction (Firefox bug 1865207).

Removals

• Removed support for the CSS-moz-user-focus property (Firefox bug 1871745 andFirefox bug 1868552).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Fixed a bug that preventedPerform Actions to correctly synthesize double and other multi-click events for themouse input source (Firefox bug 1864614). Additionally, these events will only be emitted when the actual mouse position has not changed since the last click action (Firefox bug 1681076).
• The definitions for thePause andEqual (Numpad block) keys have been updated to align with the WebDriver specification (Firefox bug 1863687).

WebDriver BiDi

• The serialization ofWindowProxy remote objects now also works correctly for out-of-process iframes (Firefox bug 1867667).
• ThebrowsingContext.setViewport command now distinguishes betweenundefined andnull as values for theviewport argument. If set toundefined, it signifies that the viewport should remain unchanged, while usingnull will reset it to its original dimensions (Firefox bug 1865618).
• Support for thebrowsingContext.traverseHistory command has been introduced, enabling navigations backward and forward in the browser history (Firefox bug 1841018).
• Fixed a bug in all supported network events where thecontext id consistently reported the top-level browsing context, even when the navigation occurred within an iframe (Firefox bug 1869735).

Marionette

• Fixed a bug withGet Element Text, where the command was incorrectly returning an empty text when the element was located within a ShadowRoot's slot (Firefox bug 1824664).

Experimental web features

These features are newly shipped in Firefox 122 but are disabled by default. To experiment with them, search for the appropriate preference on theabout:config page and set it totrue. You can find more such features on theExperimental features page.

• Declarative shadow DOM:dom.webcomponents.shadowdom.declarative.enabled.

  The<template> element now supports ashadowrootmode attribute which can be set to eitheropen orclosed, the same values as themode option of theattachShadow() method. It allows the creation of a shadow DOM subtree declaratively. (Firefox bug 1712140)

• Clonable option and property for shadow DOM.

  • TheElement.attachShadow() method now supports theclonable boolean option that specifies whether the created shadow root is clonable: the default value isfalse but when set totrue, the shadow host cloned withNode.cloneNode() orDocument.importNode() will include shadow root in the copy.
  • TheShadowRoot interface now supports theclonable read-only property. It returnstrue if the shadow root is clonable, andfalse otherwise. It always returnstrue for shadow roots created via declarative shadow DOM.

  When shadow root is created via declarative shadow DOM, theclonable option is set totrue by default, and theclonable property returnstrue. (Firefox bug 1868428)

• Popover API:dom.element.popover.enabled.

  Displaying popovers on top of page content is now supported via HTML attributes or JavaScript API, including styling with the CSS:popover-open pseudo-class and extended support for the::backdrop pseudo-element. See thePopover API reference for more details. (Firefox bug 1823757)

• Clipboard read and write:dom.events.asyncClipboard.clipboardItem,dom.events.asyncClipboard.readText anddom.events.asyncClipboard.writeText.

  The asyncClipboard API is now fully supported, includingread(),readText(), andwrite() methods and theClipboardItem interface. A paste context menu will appear for the user to confirm when reading clipboard data not provided by the same-origin page. (Firefox bug 1809106)

• Intl.Segmenter: enabled by default only in Firefox Nightly.

  TheIntl.Segmenter object allows accurate locale-sensitive text segmentation of a string. For example, to split a text into words in a language that doesn't use spaces to separate them:Intl.Segmenter("ja-JP", { granularity: "word" }). (Firefox bug 1423593)