Firefox 24 for developers

Changes for Web developers

CSS

• The two values -moz-zoom-in and -moz-zoom-out of the cursor property have been unprefixed to zoom-in and zoom-out (bug 772153).
• To match the specification, the keywords not, only, and, and or cannot be used as media types anymore (bug 757554).

HTML

• The <track> element has been implemented behind the media.webvtt.enabled preference, and is disabled by default. (bug 833385).

JavaScript

• Arrow functions are no longer automatically in strict mode unless explicitly requested with "use strict" (bug 852762).
• The String.prototype.repeat JS method has been implemented (bug 815431).
• The Set.prototype.values(), Set.prototype.keys() and Set.prototype.entries() methods on Set objects have been implemented (bug 869996).

DOM

• Support for the Range() constructor has been added (bug 868999).
• Support for the Text() constructor has been added (bug 869000).
• Support for the Comment() constructor has been added (bug 869006).
• Support for the DocumentFragment() constructor has been added (bug 869002).
• The FocusEvent interface has been implemented (bug 855741).
• Support for the ChildNode.remove() method has been added (bug 856629).
• The WebVTT interfaces related to the <track> element, HTMLTrackElement, TextTrack, TextTrackCue, TextTrackList, and TextTrackCueList have been implemented behind the media.webvtt.enabled property, defaulting to false (bug 833385).
• The Gamepad interface, and Navigator.getGamepads have been implemented behind the dom.gamepad.enabled property, defaulting to false (bug 690935).
• On desktop Firefox only, HTMLCanvasElement.getContext() can now take the webgl value, in addition to experimental-webgl (bug 870232).
• The non-standard method mozLoadFrom() of HTMLMediaElement has been removed (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 //@ (bug 870361).

MathML

• The dir attribute for controlling directionality of formulas on e.g. <math> or <mrow> elements is now equivalent to using the direction CSS property.
• The equal sign ("=") is now stretchable.
• The "updiagonalarrow" value for the notation attribute on <menclose> elements has been added.

Changes for add-on and Mozilla developers

• Doc Shells have now the allowMedia attribute to disable media playing (bug 759964).
• Sherlock search plugins in the application directory or profile  won't be loaded anymore (bug 862143).

See also

• Firefox 24 Aurora Notes
• Site Compatibility for Firefox 24

Older versions