Experimental features in Firefox

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.

Editor's note: When adding features to these tables, please try to include a link to the relevant bug or bugs using the bug macro.

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.

See bug 840640 for more details.

Disabled
(available since 53)
Disabled
(available since 53)
Disabled
(available since 53)
Disabled
(available since 53)
dom.dialog_element.enabled

CSS

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
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 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.

See bug 1223880 for more details.
Disabled
(available since 50)
Disabled
(available since 50)
Disabled
(available since 50)
Disabled
(available since 50)
layout.css.initial-letter.enabled
text-underline-position
Sets the position of an underline specified on the element.

See bug 770780 for more details.
Enabled
(available since 73)
Disabled
(available since 73)
Disabled
(available since 73)
No layout.css.text-underline-position.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.

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

WebGL draft extensions:

Disabled
(available since 67)
Disabled
(available since 67)
Disabled
(available since 67)
Disabled
(available since 67)
webgl.enable-draft-extensions

DOM

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
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.
Disabled Disabled Disabled Disabled media.setsinkid.enabled
Document.autoplayPolicy
Document.autoplayPolicy returns a string indicating how the browser handles requests to automatically play media (either using the autoplay property on a media element or by attempting to trigger playback from JavaScript code. The spec for this API is still being written. The value changes over time depending on what the user is doing, their preferences, and the state of the browser in general. Potential values include allowed (autoplay is currently permitted), allowed-muted (autoplay is allowed but only with no—or muted—audio), and disallowed (autoplay is not allowed at this time).
Disabled
(available since 66)
Disabled
(available since 66)
Disabled
(available since 66)
Disabled
(available since 66)
dom.media.autoplay.autoplay-policy-api
GeometryUtils.getBoxQuads()
Returns the CSS boxes for a Node relative to any other Node (or viewport).

See bug 917755 for more details.
Enabled
(Available since 31)
Disabled
(Available since 31)
Disabled
(Available since 31)
Disabled
(Available since 31)
layout.css.getBoxQuads.enabled
GeometryUtils.convertPointFromNode(),
GeometryUtils.convertRectFromNode(), and
GeometryUtils.convertQuadFromNode()

Maps a point, rectangle or quadruple from a given node to another one.

See bug 918189 for more details.
Enabled
(Available since 31)
Disabled
(Available since 31)
Disabled
(Available since 31)
Disabled
(Available since 31)
layout.css.convertFromNode.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
(Available since version 33)
Disabled
(Available since version 33)
Disabled
(Available since version 33)
Disabled
(Available since version 33)
media.track.enabled
Payment Request API
Provides a web API for handling web-based payments.

The UI is currently inoperative due to a bug arising after UI tests. Disabled and work put on hold.
Disabled
(available since 55)
Disabled
(available since 55)
Disabled
(available since 55)
Disabled
(available since 55)
dom.payments.request.enabled
dom.payments.request.supportedRegions
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
dom.payments.request.supportedRegions
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

WebRTC and media

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Promise-based asynchronous append and remove of buffers to a SourceBuffer object using appendBufferAsync() and removeAsync(). Disabled
(available since 62)
Disabled
(available since 62)
Disabled
(available since 62)
Disabled
(available since 62)
media.mediasource.experimental.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.
Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)
Disabled
(available since 59)
security.mixed_content.block_object_subrequest
"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

See bug 1335970 for more details.
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

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.

See bug 1435733 for more details.
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 65)
Disabled
(available since 65)
Disabled
(available since 65)
Disabled
(available since 65)
dom.security.featurePolicy.header.enabled
target="_blank" on anchors implying rel="noopener" (bug 1503681)
Following Safari's lead, we are experimenting with making target="_blank" set on an <a> element imply rel="noopener" as a security measure. the idea is that web developers would then have to explicitly request an opener relationship using rel="opener".
Enabled
(available since 65)
Enabled
(available since 65)
Enabled
(available since 65)
Disabled
(available since 65)
dom.targetBlankNoOpener.enabled
Disabling TLS 1.0 and 1.1
TLS 1.0 and 1.1 are deprecated, and all major browsers aim to remove them in Q1 2020. They are already disabled in Firefox Nightly 71 (see bug 1579270). See also TLS 1.0 and 1.1 are now deprecated, disabled in Nightly for more details.
Set to 3
(since 71)
Set to 3
(since 71)
Set to 3
(since 71)
Set to 1 security.tls.version.min (set to 3 for TLS 1.2)

Developer Tools

Feature Firefox Nightly Firefox Developer Edition Firefox Beta Firefox Release Preference
Color scheme simulation
Adds an option to simulate different color schemes allowing to test prefer-color-scheme media queries.

See bug 1550804 for more details.
Disabled
(available since 72)
Disabled
(available since 72)
Disabled
(available since 72)
Disabled
(available since 72)
devtools.inspector.color-scheme-simulation.enabled
Eager evaluation
Displays the results of the things you type into the console while you're typing.

See bug 1460518 for more details.
Disabled
(available since 73)
Disabled
(available since 73)
Disabled
(available since 73)
No devtools.webconsole.input.eagerEvaluation

See also