index.md

---

title: Firefox 24 for developers
slug: Mozilla/Firefox/Releases/24

---

{{FirefoxSidebar}}

Changes for Web developers

CSS

• The two values -moz-zoom-in and -moz-zoom-out of the {{cssxref("cursor")}} property have been unprefixed to zoom-in and zoom-out (Firefox bug 772153).

• To match the specification, the keywords not, only, and, and or cannot be used as media types anymore (Firefox bug 757554).

HTML

• The {{HTMLElement("track")}} element has been implemented behind the media.webvtt.enabled preference, and is disabled by default. (Firefox bug 833385).

JavaScript

• Arrow functions are no longer automatically in strict mode unless explicitly requested with "use strict" (Firefox bug 852762).

• The String.prototype.repeat JS method has been implemented (Firefox bug 815431).

• The {{jsxref("Set.prototype.values()")}}, {{jsxref("Set/values", "Set.prototype.keys()")}} and {{jsxref("Set.prototype.entries()")}} methods on {{jsxref("Set")}} objects have been implemented (Firefox bug 869996).

DOM

• Support for the {{domxref("Range.Range", "Range()")}} constructor has been added (Firefox bug 868999).

• Support for the {{domxref("Text.Text", "Text()")}} constructor has been added (Firefox bug 869000).

• Support for the {{domxref("Comment.Comment", "Comment()")}} constructor has been added (Firefox bug 869006).

• Support for the {{domxref("DocumentFragment.DocumentFragment", "DocumentFragment()")}} constructor has been added (Firefox bug 869002).

• The {{domxref("FocusEvent")}} interface has been implemented (Firefox bug 855741).

• Support for the {{domxref("ChildNode.remove()")}} method has been added (Firefox bug 856629).

• The WebVTT interfaces related to the {{HTMLElement("track")}} element, {{domxref("HTMLTrackElement")}}, {{domxref("TextTrack")}}, {{domxref("TextTrackCue")}}, {{domxref("TextTrackList")}}, and {{domxref("TextTrackCueList")}} have been implemented behind the media.webvtt.enabled property, defaulting to false (Firefox bug 833385).

• The {{domxref("Gamepad")}} interface, and {{domxref("Navigator.getGamepads")}} have been implemented behind the dom.gamepad.enabled property, defaulting to false (Firefox bug 690935).

• On desktop Firefox only, HTMLCanvasElement.getContext() can now take the webgl value, in addition to experimental-webgl (Firefox bug 870232).

• The non-standard method mozLoadFrom() of {{domxref("HTMLMediaElement")}} has been removed (Firefox bug 877135).

Developer Tools

• The Network inspector now lets you filter by content type (CSS/image/font etc.) and see the relevant size and load times.

• The Devtools options panel to the left lets you disable/enable JavaScript temporarily.

• Extension developers may use the new Browser Console for Chrome-level scripts (Replaces Error Console).

• The source map syntax has been changed to use //# instead of //@ (Firefox bug 870361).

MathML

• The dir attribute for controlling directionality of formulas on e.g. {{MathMLElement("math")}} or {{MathMLElement("mrow")}} elements is now equivalent to using the {{cssxref("direction")}} CSS property.

• The equal sign ("=") is now stretchable.

• The "updiagonalarrow" value for the notation attribute on {{MathMLElement("menclose")}} elements has been added.

Changes for add-on and Mozilla developers

• Doc Shells have now the allowMedia attribute to disable media playing (Firefox bug 759964).

• Sherlock search plugins in the application directory or profile won't be loaded anymore (Firefox bug 862143).

See also

• Firefox 24 Aurora Notes

Older versions

{{Firefox_for_developers('23')}}