Firefox 153 release notes for developers (Beta)

Changes for web developers

Developer Tools

• The developer tools now provide the heading level for a heading element in the accessibility highlighter and accessibility tree (previously just the fact that it was a heading was shown). The information can be found in the Accessibility Inspector panel. (Firefox bug 1588784 and Firefox bug 2044904).

HTML

• HTML parsing rules for <select> elements have been updated to allow all nested elements to be parsed into DOM rather than just <option>, <optgroup>, and <hr>. This enables possible future support of customizable select elements. (Firefox bug 2019977).

CSS

• The ::-webkit-scrollbar pseudo-element selector is now recognized, so the @supports selector(::-webkit-scrollbar) check returns true. Note that this reports the selector as supported even though scrollbar styling via ::-webkit-scrollbar is not truly implemented. This was added to fix an issue where scrollbars of nested scrollable areas could stack on top of each other. For example, when a scrollbar is set to display: none or width: 0 leaving some content unreachable. (Firefox bug 2038877).

JavaScript

• The TC39 Intl.Locale info proposal is now supported. This includes all the instance methods on Intl.Locale that are prefixed with "get" — getCalendars(), getCollations(), getHourCycles(), getNumberingSystems(), getTextInfo(), getTimeZones(), and getWeekInfo(). (Firefox bug 2037069).
• The Error.stackTraceLimit static data property is supported for setting or getting the maximum number of stack frames captured in an error stack trace. Setting the value smaller than the default can improve performance. (Firefox bug 2037856).
• Text modules can now be imported into a string using with { type: "text" }. Unlike for JavaScript or CSS modules, the media type of the response is ignored, and the content is parsed as text even if the file contains scripts or other executable code. (Firefox bug 2039881).
• The import source syntax (part of the TC39 source phase imports proposal) is now supported. It is similar to the normal import declaration, but instead of loading and evaluating a module, it produces an object representing the module's source code that can be evaluated later. Note that this feature is not yet useful for developers, as only the syntax is currently supported: the source representation of WebAssembly modules is implemented separately and is not yet available. (Firefox bug 2043242).

APIs

• The IDBObjectStore.getAllRecords() and IDBIndex.getAllRecords() methods are now supported. These retrieve all records (or a specified subset of records) from an object store and index, respectively. (Firefox bug 1927945).
• The Picture-in-Picture API is now supported on desktop platforms. This provides a convenient mechanism for websites to toggle display of a <video> element between a page and a floating always-on-top video window, allowing users to continue watching while they interact with other sites or applications. (Firefox bug 1463402).

DOM

• The Popover API now has more consistent behavior when hint and auto popovers are opened and closed. This follows the specification update in whatwg/html#12345. (Firefox bug 2029974).

Media, WebRTC, and Web Audio

• The RTCDtlsTransport.getRemoteCertificates() method gets the certificates used by the remote peer to secure the DTLS communication. These can be used for application-layer authentication of a remote peer. (Firefox bug 1805446).
• The decodingInfo() and encodingInfo() methods of the MediaCapabilities interface now accept the "webrtc" configuration type. This allows a site to query whether a given audio or video configuration can be decoded or encoded using WebRTC, and whether doing so will be smooth, power efficient, or both. Support for the non-standard transmission type, which was used as an alias for webrtc, is removed. (Firefox bug 2037610 and Firefox bug 2032075).
• All mandatory and some optional WebRTC "transport" statistics can now be reported in a RTCStatsReport. The returned object is a RTCTransportStats with the following properties: dtlsCipher, dtlsRole, dtlsState, iceLocalUsernameFragment, iceRole, iceState, id, selectedCandidatePairId, srtpCipher, timestamp, tlsVersion, and type. In addition the transportId property is now available on RTCOutboundRtpStreamStats, RTCRemoteOutboundRtpStreamStats, RTCRemoteInboundRtpStreamStats and RTCInboundRtpStreamStats. (Firefox bug 1225723 and Firefox bug 2019389).

WebAssembly

• JavaScript Promise Integration (JS-PI) is now enabled, allowing WebAssembly modules to interoperate with asynchronous, Promise-based JavaScript APIs. This lets WebAssembly code suspend while waiting for a JavaScript promise and resume when the promise settles. See WebAssembly.Suspending for an explanation and working example. (Firefox bug 2044809).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Improved the window manipulation commands in Marionette and WebDriver BiDi to allow individual window geometry properties, such as x, y, width, and height, to be adjusted independently. (Firefox bug 1941404).
• Fixed a bug where click and pointer action commands could fail if the element's first DOMRect (e.g., inline elements spanning multiple lines) was zero-sized. (Firefox bug 2038932).
• Restricted navigation to privileged pages (certain about:* pages, chrome://, and resource:// URLs) when operating in content scope. (Firefox bug 1579790).

WebDriver BiDi

• Extended the emulation.setLocaleOverride command to also apply a locale emulation to dedicated and shared workers. (Firefox bug 2015655).
• Extended the emulation.setTimezoneOverride command to also apply a timezone emulation to dedicated and shared workers. (Firefox bug 2015657).
• Updated the browsingContext.create command to no longer emit browsingContext.domContentLoaded and browsingContext.load events for the initial about:blank page when creating new top-level browsing contexts, and to now emit the browsingContext.contextCreated event at the end of the creation process. (Firefox bug 1930594).
• Fixed a bug where functions created by the script.addPreloadScript command might have stopped working after several navigations. (Firefox bug 2046390).

Marionette

• Fixed the Take Element Screenshot command from WebDriver Classic to crop screenshots of elements which exceed the viewport. (Firefox bug 2013176).
• Fixed the Perform Actions command to properly await internal action finalization, preventing potential race conditions. (Firefox bug 2031596).

Changes for add-on developers

• Extensions now require explicit user permission to access file:// URLs. Previously, access to local files was covered by the "Access your data for all websites" host permission. This change introduces a separate "Access local files on your computer" option in the extension's permissions settings (desktop only), and file access is turned off by default for all extensions, including existing ones. The extension.isAllowedFileSchemeAccess() method now correctly returns true if the user has granted file scheme access; previously, Firefox always returned false. Additionally, calling devtools.inspectedWindow.eval() on file:// URLs now requires this permission. (Firefox bug 2034168)
• Supports the userScripts.execute() method, enabling extensions to inject user scripts on demand into a tab or frame. Unlike userScripts.register(), this method supports one-off injection of multiple script sources executed in a defined order. (Firefox bug 1930776)
• Adds the publicSuffix API, enabling extensions to determine the registrable domain (eTLD+1) and public suffix of a hostname using the browser's built-in Public Suffix List. The API provides three synchronous methods: publicSuffix.isKnownSuffix(), publicSuffix.getKnownSuffix(), and publicSuffix.getDomain(). (Firefox bug 1315558)
• Extension content scripts can now read and modify constructed stylesheets in document.adoptedStyleSheets and ShadowRoot.adoptedStyleSheets, without .wrappedJSObject. (Firefox bug 1751346)
• Adds documentId to a range of WebExtension APIs, including a new runtime.getDocumentId() method, webNavigation events and methods, webRequest events, scripting injection targets, and messaging APIs. See Work with documentId for the full list of supported events and methods, along with guidance on using documentId. (Firefox bug 1891478)
• For contextual identities (containers):
  • Adds the contextualIdentities.getSupportedColors() and contextualIdentities.getSupportedIcons() methods to retrieve the supported colors and icons, avoiding the need to hardcode those values. (Firefox bug 2044712)
  • Updates the colors available. "turquoise" is renamed to "cyan", "toolbar" is renamed to "gray", and "violet" is added. The legacy names "turquoise" and "toolbar" are accepted for backward compatibility. To avoid hardcoding color names, use contextualIdentities.getSupportedColors() to retrieve the available colors. (Firefox bug 2044354)

Experimental web features

These features are shipping in Firefox 153 but are disabled by default. To experiment with them, search for the appropriate preference on the about:config page and set it to true. You can find more such features on the Experimental features page.

• JPEG XL image support (Nightly): image.jxl.enabled

  The Rust-based JPEG XL image decoder is now enabled by default in Nightly. (Firefox bug 2040074).

• Tree counting CSS functions: layout.css.tree-counting-functions.enabled

  The sibling-count() and sibling-index() function are now supported. The sibling-count() function returns the number sibling elements as well as the element itself. The sibling-index() function returns the index number of the element in relation to its siblings, this starts from 1 and not 0. (Firefox bug 2042063).