Firefox 138 for developers

Removals

Removals

• The Error.captureStackTrace() static method is now supported. This installs stack trace information on a provided object as the Error.stack property. Its main use case is to install a stack trace on a custom error object that does not derive from the Error interface. (Firefox bug 1950508).
• The Error.isError() static method can now be used to check whether or not an object is an instance of an Error or a DOMException. This is more reliable than using instanceof for the same purpose. (Firefox bug 1952249).

Removals

Removals

• The HTTP Origin-Agent-Cluster response header can now be used by a site to hint that the associated document should be placed in an origin-keyed agent cluster. When in such a cluster, the operating system process and/or other OS resources used by the document are only shared with other documents from the same origin. This makes it less likely that a resource-intensive document will degrade the performance of documents from other origins. Developers can test whether the browser has put the document in an origin-keyed agent cluster using the window.originAgentCluster property. (Firefox bug 1665474)

Removals

Removals

DOM

Media, WebRTC, and Web Audio

• WebRTC applications can now set a preference for prioritizing framerate or resolution when both cannot be maintained at the configured levels due to network degradation. The value is set using the degradationPreference property in the parameter object passed to the setParameters() method of the RTCRtpSender interface. It can also be read from the object returned by the getParameters() method. (Firefox bug 1329847).

Removals

Removals

General

WebDriver BiDi

Marionette

• Support provided for page_action as a menus.ContextType in the menus API for Manifest V3 extensions. This provides Manifest V3 extensions the same ability as Manifest V2 extensions to add menu items to page_action. (Firefox bug 1951166)
• The contextualIdentities API is no longer defined in Firefox for Android. Previously, it was defined but defective. (Firefox bug 1659500)
• The contextualIdentities permission is now not recognized on Firefox for Android. Previously, it enabled a broken version of the "containers" feature. (Firefox bug 1659500)
• The new Manifest V3 version of the userScripts API is now available on Firefox for Android. (Firefox bug 1949955)
• The alarms.create API now returns a Promise instead of undefined. (Firefox bug 1869171)

These features are newly shipped in Firefox 138 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.

• ::details-content CSS pseudo-element: layout.css.details-content.enabled. The CSS ::details-content pseudo-element enables you to style the content of the <details> element (Firefox bug 1901037).
• MutationEvent on path to removal: MutationEvent and its associated events (DOMSubtreeModified, DOMNodeInserted, DOMNodeRemoved, DOMCharacterDataModified,DOMAttrModified) are now disabled on Firefox Nightly by default. (Firefox bug 1951772).
• Notification.actions: (Nightly release): The Notification.actions property can get the actions associated with a Notification, as set using ServiceWorkerRegistration.showNotification(). (Firefox bug 1225110).