Firefox 97 for developers

No notable changes

• The CSS units cap and ic are now supported for use with <length> and <length-percentage> data types. For more information, see Firefox bug 1702924 and Firefox bug 1531223.
• The CSS property color-adjust has been renamed to print-color-adjust to match the relevant specification. The color-adjust shorthand name is deprecated. See Firefox bug 747595 for details.
• CSS cascade layers are now available by default. The @layer rule declares a cascade layer, which allows declaration of styles and can be imported via the @import rule using the layer() function. See Firefox bug 1699217 for more details.
• The global CSS keyword revert-layer has been added to allow rolling back of property values in one cascade layer to the matching rules in the previous cascade layer. This keyword can be applied on any property, including the CSS shorthand property all. For more information, see Firefox bug 1699220.
• The CSS scrollbar-gutter property is now supported. This gives developers control over reserved space for the scrollbar, preventing unwanted layout changes as the content grows. See Firefox bug 1715112 for more details.

No notable changes

• The SVG d attribute, used to define a path to be drawn, can now be used as a property in CSS. It accepts the values path() or none. (See Firefox bug 1744599 for details.)

Removals

• A number of SVGPathSeg APIs are now disabled by default behind a preference, and are expected to be removed in future revisions. This includes: SVGPathSegList, SVGPathElement.getPathSegAtLength(), SVGAnimatedPathData. (See Firefox bug 1388931 for more details.)

• AnimationFrameProvider is now available in a DedicatedWorkerGlobalScope. This means the requestAnimationFrame and cancelAnimationFrame methods can be used within a dedicated worker. (See Firefox bug 1388931 for more details.)

DOM

• The reason for an abort signal can now be set using AbortController.abort() (or AbortSignal.abort()), and will be available in the AbortSignal.reason property. This reason defaults to being an "AbortError" DOMException. The reason can be thrown or handled via promise rejection as appropriate. (Firefox bug 1737771).
• The convenience method AbortSignal.throwIfAborted() can be used to check if a signal has been aborted, and if so throw the AbortSignal.reason(). This makes it easier for developers to handle abort signals in code where you can't simply pass the signal to an abortable method. (Firefox bug 1745372).

• Marionette:Quit accepts a new boolean parameter, safeMode, to restart Firefox in safe mode (Firefox bug 1144075).
• Improved stability for WebDriver:NewSession and WebDriver:NewWindow when waiting for the current or initial document to be loaded (Firefox bug 1739369, Firefox bug 1747359).

• cookieStoreId in tabs.query supports an array of strings. This enables queries to match tabs against more than one cookie store ID (Firefox bug 1730931).
• cookieStoreId added to contentScripts.register. This enables extensions to register container-specific content scripts (Firefox bug 1470651).