In order to test new features, Mozilla publishes a test version of the Firefox browser, Firefox Nightly, every day. Experimental features, for example implementations of proposed Web platform standards, are available. This page lists features that are in Nightly versions of Firefox along with information on how to activate them, if necessary. You can test your Web sites and applications before these features get released and ensure everything will still work with the latest Web technology capabilities.

To test these experimental features, you need to download Firefox Nightly or Firefox Developer Edition.

HTML

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
<dialog>
Dialog element including DOM APIs to interact with it. Implementation of modal dialogs and accessibility still missing.
Disabled
(available since 53)
Disabled
(available since 53)
--- --- dom.dialog_element.enabled
Disabling Firefox-only editing features
Some rich-text editing features have been disabled by default, for better cross-browser compatibility. These are object resizing on <img>, <table>, and absolutely-positioned elements; inline table editing to add or remove rows and columns; and the grabber that allows moving of absolutely-positioned elements (bug 1449564).
Disabled Disabled Disabled Enabled editor.resizing.enabled_by_default
editor.inline_table_editing.enabled_by_default
editor.positioning.enabled_by_default

CSS

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Subgrids Disabled
(recognized but not implemented yet)
Disabled
(recognized but not implemented yet)
Disabled
(recognized but not implemented yet)
Disabled
(recognized but not implemented yet)
layout.css.grid-template-subgrid-value.enabled
Display stray control characters in CSS as hex boxes
This feature renders control characters (Unicode category Cc) other than tab (U+0009), line feed (U+000A), form feed (U+000C), and carriage return (U+000D) as a hexbox when they are not expected.
Enabled
(available since 43)
Disabled
(available since 43)
Disabled
(available since 43)
Disabled
(available since 43)
layout.css.control-characters.enabled or layout.css.control-characters.visible

The font-variation-settings property
The font-variation-settings provides low-level control over OpenType or TrueType font typographic features, by specifying the four letter axis names of the features you want to vary, along with their variation values.

Enabled
(available since 53)
Enabled
(available since 53)
Enabled
(available since 53)
Disabled
(available since 53)

layout.css.font-variations.enabled

For the downloadable fonts on axis-praxis, you also need gfx.downloadable_fonts.keep_variation_tables (in Firefox 54 and later).

The font-variation-settings descriptor
A descriptor version of font-variation-settings that goes inside @font-face.
Enabled
(available since 60)
Enabled
(available since 60)
Enabled
(available since 60)
Disabled
(available since 60)
layout.css.font-variations.enabled
 
The contain CSS property
The contain CSS property is part of the CSS Containment Module Level 1 specification and allows you to indicate that an element and its contents are independent of the rest of the document tree, allowing user agents to optimize the rendering of a page.
Disabled
(available since 45)
Disabled
(available since 45)
Disabled
(available since 45)
Disabled
(available since 45)
layout.css.contain.enabled

The column-span CSS property
The column-span CSS property is part of the CSS Multi-column Layout Module specification and allows you to specify how many columns an element spans across.

Firefox currently only parses the property (bug 1339298), it's not actually implemented yet (bug 616436).

Disabled
(recognized since 55, but not implemented yet)
Disabled
(recognized since 55, but not implemented yet)
Disabled
(recognized since 55, but not implemented yet)
Disabled
(recognized since 55, but not implemented yet)
layout.css.column-span.enabled
The frames() timing function
See The frames() class of timing-functions for more details.
Enabled N/A Disabled
(available since 55)
Disabled
(available since 55)
None
The ::slotted pseudo-element
Selects elements when they are inserted into a <slot> in an HTML <template>.
Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)
dom.webcomponents.customelements.enabled and dom.webcomponents.shadowdom.enabled
Individual transform properties
translate, scale, and rotate. These specify transforms individually and independently of the transform property.
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)
layout.css.individual-transform.enabled
The initial-letter CSS property
The initial-letter CSS property is part of the CSS Inline Layout specification and allows you to specify how dropped, raised, and sunken initial letters are displayed.
Disabled
(available since 50)
Disabled
(available since 50)
Disabled
(available since 50)
Disabled
(available since 50)
layout.css.initial-letter.enabled
The Motion Path properties
The Motion Path Module Level 1 specification defines the offset-path, offset-distance, offset-position, offset-rotate, offset-anchor, and offset CSS properties, which allow to position and animate elements along a path.
Enabled
(available since 63)
Disabled
(available since 63)
Disabled
(available since 63)
No layout.css.motion-path.enabled
-webkit-appearance alias for -moz-appearance
We've added this alias for web compatibility purposes, and are currently testing it out before final release.
Enabled
(available since 63)
Enabled
(available since 63)
Enabled
(available since 63)
Disabled
(available since 63)
layout_css_webkit_appearance_enabled

Function syntax for @supports
The new function syntax for @supports allows you to test whether a selector is supported and apply CSS accordingly.

Enabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
layout.css.supports-selector.enabled
clip-path: path()
Supporting path() values on the clip-path property.
Disabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
layout.css.clip-path-path.enabled

JavaScript

See also ECMAScript Next support for implemented features of ECMAScript 2016 and later, that are not experimental and thus available without preferences in Firefox Release.

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Additions to the ArrayBuffer object
Adds the ArrayBuffer.transfer() that returns a new ArrayBuffer whose contents have been taken from the oldBuffer's data (spec).
36 Disabled Disabled Disabled None
TypedObject objects (spec) Enabled Disabled Disabled Disabled None

APIs

Canvas & WebGL

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
OffscreenCanvas
The OffscreenCanvas interface provides a canvas that can be rendered off screen. It is available in both the window and worker contexts.
Disabled
(available since 44)
Disabled
(available since 44)
Disabled
(available since 44)
Disabled
(available since 44)
gfx.offscreencanvas.enabled
Hit regions
Whether the mouse coordinates are within a particular area on the canvas is a common problem to solve. The hit region API allows you define an area of your canvas and provides another possibility to expose interactive content on a canvas to accessibility tools.
Disabled
(available since 30)
Disabled
(available since 30)
Disabled
(available since 30)
Disabled
(available since 30)
canvas.hitregions.enabled
Streams API
Allows JavaScript to programmatically access streams of data received over the network and process them as desired by the developer.
Disabled
(available since 57)
Disabled
(available since 57)
Disabled
(available since 57)
Disabled
(available since 57)
dom.streams.enabled and javascript.options.streams

DOM

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
HTMLMediaElement.seekToNextFrame()
Part of an experimentation process around support non-real-time access to media for tasks including filtering, editing, and so forth, the HTMLMediaElement.seekToNextFrame() advances the the current play position to the next frame in the media.
49
(Fundamental update in version 50)
49
(Fundamental update in version 50)
Disabled Disabled media.seekToNextFrame.enabled
HTMLMediaElement.allowedToPlay()
A proposed addition to HTMLMediaElement whose Boolean value is true if the browser is able to play the media without its being blocked by autoplay blocking policies, mute functionality, or the like. Details of what constitutes blocking may vary from browser to browser.
Enabled
(available since 63)
No No No  
HTMLMediaElement.setSinkId
Allows you to set the sink ID of an audio output device on an HTMLMediaElement, thereby changing where the audio is being output.
Enabled Disabled Disabled Disabled media.setsinkid.enabled
GeometryUtils.getBoxQuads() (bug 917755) 31 31 Disabled Disabled layout.css.getBoxQuads.enabled
GeometryUtils.convertPointFromNode(),
GeometryUtils.RectFromNode(), and
GeometryUtils.convertQuadFromNode()
(bug 918189)
31 31 Disabled Disabled layout.css.convertFromNode.enabled
Node.rootNode
The Node.rootNode property returns a Node object representing the topmost node in the tree, or the current node if it's the topmost node in the tree.
This feature is kept experimental as its naming poses Web compatibility problems. It will be renamed in the future.
48 48 Disabled Disabled dom.node.rootNode.enabled
Support for multiple audio and video tracks
Implements HTMLMediaElement.audioTracks and HTMLMediaElement.videoTracks.
Firefox doesn't support multiple audio or video tracks, preventing the most common use cases for these properties to work properly. That's why these properties are not activated by default in any version.
Disabled
(Experimental implementation since version 33)
Disabled Disabled Disabled media.track.enabled
Better value for Event.timestamp
The property Event.timestamp is returning a DOMHighResTimeStamp, which is now relative to the Unix epoch.
32 (Windows)
43 (Linux)
32 (Windows)
43 (Linux)
Disabled Disabled media.track.enabled
PromiseRejectionEvent and related features
Providing a way to monitor and more finely control the rejection of Promises.
Disabled
(available since 55)
Disabled Disabled Disabled dom.promise_rejection_events.enabled
Payment Request API
Provides a web API for handling web-based payments.
Disabled
(available since 55)
Disabled
(available since 55)
Disabled
(available since 55)
Disabled
(available since 55)
dom.payments.request.enabled
Basic Card Payment API
Provides dictionaries that define data structures describing card payment types and payment responses for use in the Payment Request API. See BasicCardRequest and BasicCardResponse.
Disabled
(available since 56)
Disabled
(available since 56)
Disabled
(available since 56)
Disabled
(available since 56)
dom.payments.request.enabled
Window.content only available to Chrome code
The proprietary Window.content property is now only available to chrome (privileged) code, and not available to the web anymore (bug 864845).
Enabled
(since 57)
Disabled Disabled Disabled  

CSSStyleDeclaration.getPropertyCSSValue() has been deprecated
Use CSSStyleDeclaration.getPropertyValue() instead.

Disabled
(since 61)
Disabled
(since 61)
Disabled
(since 61)
Enabled  
Autodirectional Scroll Wheel
Using a single-direction scroll wheel inside a target that can only be scrolled in one direction always scrolls in that direction, regardless of the directionality of the wheel itself.
Disabled
(available since 61)
Disabled
(available since 61)
Disabled
(available since 61)
Disabled
(available since 61)
mousewheel.autodir.enabled
VisualViewport API
Provides access to information about the visual viewport of a given window.
Disabled
(available since 63)
Disabled
(available since 63)
Disabled
(available since 63)
Disabled
(available since 63)
dom.visualviewport.enabled

Storage Access API
Allows third party embedded content to request access to the document's first party storage.

Disabled
(available since 65)
Disabled
(available since 65)
Disabled
(available since 65)
Disabled
(available since 65)
dom.storage_access.enabled

WebRTC and media

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
AV1 media playback support
Support for playback of video encoded using the Alliance for Open Media AOMedia Video 1 (AV1) format.
Disabled
(available since 55; disabled by default in 61)
Disabled
(available since 55; disabled by default in 61)
Disabled Disabled media.av1.enabled
Promise-based asynchronous append and remove of buffers to a SourceBuffer object using appendBufferAsync() and removeAsync(). Disabled
62
No No No media.mediasource.experimental.enabled

Developer Tools

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Flexbox Inspector
Allows to inspect Flexbox layouts and highlights flex items within the page.
Enabled
(available since 58; enabled by default since 63)
Disabled
(available since 58)
Disabled
(available since 58)
Disabled
(available since 58)
devtools.flexboxinspector.enabled and devtools.inspector.flexboxHighlighter.enabled

Security

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Block plain text requests from Flash plugins on encrypted pages
A pref has been added to treat mixed OBJECT_SUBREQUESTS as active content to mitigate MitM attacks due to plugins loading "risky" content. See bug 1190623 for more details.
Enabled
(available since 59)
Enabled
(available since 59)
Enabled
(available since 59)
Disabled security.mixed_content.block_object_subrequest to true
SecurityPolicyViolationEvent, and the securitypolicyviolation event
Allows developers to programmatically respond to CSP violations.
Enabled
(available since 59)
Enabled
(available since 59)
Enabled
(available since 59)
Disabled security.csp.enable_violation_events

"Insecure connection" icon display for non-HTTPS sites
Firefox 59 has two new preferences, disabled by default, which when enabled cause a lock with a strike-through to appear in the address bar when a non-HTTPS site is loaded. This work is part of the preparation for moving to a completely HTTPS web, the idea being that in the near future insecure sites will be specially indicated, rather than secure sites.

Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)

security.insecure_connection_icon.enabled for non-private browsing

security.insecure_connection_icon.pbmode.enabled for private browsing

"Not secure" text warning for non-HTTPS sites
Following on from the above experiment, Firefox 60 has another two new preferences, disabled by default, that when enabled cause a "Not secure" text label to appear in the address bar next to the lock icon when a non-HTTP site is loaded (bug 1335970).
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)

security.insecure_connection_text.enabled for non-private browsing

security.insecure_connection_text.pbmode.enabled for private browsing

Origin header sent for non-CORS requests
To mitigate CSRF attacks, the Origin header should be sent with non-CORS requests unless they are GET or HEAD (bug 446344). We currently only send Origin on CORS requests.

Disabled Disabled Disabled Disabled network.http.sendOriginHeader

Application Cache only in secure contexts
As a precursor to disabling it altogether, Application Cache has been disabled in non-secure contexts, currently in Nightly/Beta editions of Firefox only (bug 1354175).

Since 60 Since 60 Since 60 No  
Upgrading mixed display content
As an experiment we have implemented a preference to upgrade mixed content on secure pages. When enabled, the browser shouldn't show a mixed padlock (padlock with warning triangle) as the media requests on the page have been upgraded to using https://. In addition, the console warning is different, saying that the insecure requests have been updated to HTTPS. This feature may also prevent requests from loading if the requested media doesn't support HTTPS (bug 1435733).
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)
Disabled
(available since 60)
security.mixed_content.upgrade_display_content
Feature-Policy
Feature Policy allows web developers to selectively enable, disable, and modify the behavior of certain features and APIs in the browser. It is similar to CSP but controls features instead of security behavior.
Enabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
Disabled
(available since 64)
dom.security.featurePolicy.enabled

See also

Document Tags and Contributors

Last updated by: chrisdavidmills,