Firefox 152 release notes for developers (Stable)

This article provides information about the changes in Firefox 152 that affect developers. Firefox 152 was released on June 16, 2026.

Changes for web developers

Developer Tools

• The developer tools now have a "Show comments" option to toggle the display of HTML comment nodes in the Inspector. This option can be found in the Settings panel. (Firefox bug 1455294).

HTML

No notable changes.

SVG

• The read-only property is now supported, indicating whether text is drawn on the left-hand side or right-hand side of a text path. This reflects the corresponding side attribute on the <textPath> element. (Firefox bug 2034371).

CSS

• The field-sizing CSS property lets you control the sizing behavior of form control elements. This property has two values: content allows elements to adjust in size to fit their content, and fixed sets a fixed size on elements. (Firefox bug 2036620).

JavaScript

No notable changes.

APIs

• The firstInterimResponseStart and finalResponseHeadersStart properties of the PerformanceResourceTiming interface are supported. These can be used to measure how long it takes for the browser to receive interim HTTP responses and the final HTTP response after sending a request, respectively. (Firefox bug 2006340).
• The and properties are now supported. These provide a more ergonomic way to access the associated animation than calling element.getAnimations() and filtering on the event's animationName or propertyName. (Firefox bug 1929118).

DOM

• Notification actions are supported. This includes the actions parameter of ServiceWorkerRegistration.showNotification(), and the actions read-only property and the maxActions static read-only property of the Notification interface. This allows you to include action buttons on device notifications, and react to when they're pressed. (Firefox bug 1959931).
• The Element.getAnimations() method can now accept the options.pseudoElement parameter. This allows you to directly target a specific pseudo-element, rather than filtering the results of { subtree: true }. (Firefox bug 1935557).
• The Element.requestPointerLock() method now supports the options.unadjustedMovement parameter. This allows code to disable OS-level mouse acceleration and use raw mouse input instead, which is useful in cases where slow and precise control over mouse movement is needed. (Firefox bug 2037802).

Media, WebRTC, and Web Audio

• The receiveTime property is now included in the metadata returned from RTCEncodedVideoFrame.getMetadata() and RTCEncodedAudioFrame.getMetadata(), and can be passed to the RTCEncodedVideoFrame() and RTCEncodedAudioFrame() constructors as a property in the options parameter. (Firefox bug 2033420).

WebDriver conformance (WebDriver BiDi, Marionette)

General

• Improved the Marionette and WebDriver BiDi screenshot commands to enforce maximum allowed dimensions. (Firefox bug 2020302).

WebDriver BiDi

• Extended the webExtension.install command to support installing web extensions in Firefox enabled in Private Browsing mode. (Firefox bug 1947679).
• Improved the browser.setDownloadBehavior command to allow overriding the download target folder before the temporary file is created. (Firefox bug 2017252).
• Fixed network events to only forward in-memory cached JavaScript responses when there is a matching network event collector, avoiding unnecessary data forwarding. (Firefox bug 2018237).

Marionette

• Improved the WebDriver:Navigate and WebDriver:Refresh commands to properly report errors when triggering the navigation fails, instead of silently ignoring them. (Firefox bug 2033769).

Changes for add-on developers

• The ability of extensions to dynamically execute code in their moz-extension: documents with tabs.executeScript, tabs.insertCSS, tabs.removeCSS, scripting.executeScript, scripting.insertCSS, and scripting.removeCSS has been removed. This feature was deprecated in Firefox 149. (Firefox bug 2015559)

  As an alternative, an extension can run code in its documents dynamically by registering a runtime.onMessage listener in the document's script, then sending a message to trigger execution of the required code.

Experimental web features

These features are shipping in Firefox 152 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.

• Check if a media encoding/decoding configuration is supported for WebRTC: media.mediacapabilities.webrtc.enabled

  The webrtc type can now be passed as an option for MediaCapabilities.decodingInfo() and MediaCapabilities.encodingInfo() to check if an encoding/decoding configuration can be used for WebRTC. This replaces the non-standard transmission type, which was previously used as an alias in Firefox. (Firefox bug 1825286).

• TC39 Iterator includes proposal: javascript.options.experimental.iterator_includes

  The Iterator.prototype.includes() method tests whether the iterator will produce a specified value. (Firefox bug 2025779).

• TC39 Intl.Locale info proposal: javascript.options.experimental.intl_locale_info

  The TC39 Intl.Locale info proposal is now supported on nightly builds if the preference is enabled. This includes all the Intl.Locale instance methods prefixed with "get". (Firefox bug 1693576).

• Text module import: javascript.options.experimental.import_text

  The with clause { type: "text" } allows importing a module's source as a string value. The media type of the response is ignored, and the content is parsed as text even if the source contains scripts or other executable code. (Firefox bug 2024854).

• <timeline-range-name> values in @keyframes selectors: layout.css.scroll-driven-animations.enabled

  The @keyframes at-rule now supports <timeline-range-name> values. These values let you specify the segment within which a scroll-driven animation takes place. (Firefox bug 1824875).