Firefox 20 was released on April, 2nd 2013. This article provides information about the changes in this release that will affect developers.

Changes for Web developers

HTML

• Support for thedownload attribute on the<a> and<area> element has been added (Firefox bug 676619).
• The valueauto for theglobal attributedir has been implemented (Firefox bug 548206).
• Theglobal attributecontextmenu now works on Firefox for Android (Firefox bug 736321).

JavaScript

• Support for theWeakMap.prototype.clear() method, recently added to the Harmony (ECMAScript 2015) draft proposal has been added (Firefox bug 814562).
• Support for theMath.imul() method, a C-style 32-bit multiplication function. Though proposed for Harmony (ECMAScript 2015) it has not yet been accepted and still is non-standard (Firefox bug 808148).
• Web apps using draggable text with Kinetic 3.x are working, even when using the Cairo canvas backend (Firefox bug 835064).
• Thefor each...in statement has been deprecated and should not be used. Consider using the newfor...of statement (Firefox bug 804834).
• Support for theMap.prototype.keys(),Map.prototype.values(), andMap.prototype.entries() has been added (Firefox bug 817368).

CSS

• CSS Flexbox is now available by default in pre-release builds only (excluding beta versions). It can be enabled in release and beta versions by setting thelayout.css.flexbox.enabled about:config preference totrue.
• Themask-type property has been added (Firefox bug 793617).
• Experimental support for the:scope pseudo-class has been added. Enabled by default in Aurora and Nightly, it can be enabled in release and beta versions by setting thelayout.css.scope-pseudo.enabled about:config preference totrue (Firefox bug 648722).

DOM/APIs

• HTMLMediaElement supports nowplaybackRate (both read and write), with pitch correction. Pitch correction can be controlled using the propertymozPreservesPitch (Firefox bug 495040).
• CSSOM: Support for the newCSSGroupingRule andCSSConditionRule has been added (Firefox bug 814907).
• CSSOM: OnCSSRule the constant CSSRule.MOZ_KEYFRAME_RULE and CSSRule.MOZ_KEYFRAMES_RULE have been unprefixed to CSSRule.KEYFRAME_RULE and CSSRule.KEYFRAMES_RULE. The prefixed version is temporarily kept for helping Web author to transition their codeFirefox bug 816431).
• CSSOM: It is now possible to set the value ofconditionText forCSSMediaRule (Firefox bug 815021).
• TheDOMParserparseFromStream andparseFromBuffer methods are no longer available from web content (Firefox bug 816410).
• TheXMLSerializerserializeToStream method is no longer available from web content (Firefox bug 816410).
• TextDecoder andTextEncoder interfaces are now available in Workers (Firefox bug 795542).
• Support for theCSS.supports() method has been added, behind thelayout.css.supports-rule.enabled pref (off by default) (Firefox bug 779917).
• Support for UndoManager has been added (Firefox bug 617532).
• The CSSOMDocument.caretPositionFromPoint() method, which returns aCaretPosition has been implemented.
• The index argument of theHTMLTableRowElement.insertCell() andHTMLTableElement.insertRow() methods has been made optional as per HTML specification.
• Navigator.getUserMedia, still prefixed asNavigator.mozGetUserMedia is now activated by default.
• The third, optional,transfer argument ofWindow.postMessage is now supported. It allows to transfer a sequence oftransferable objects to the destination (Firefox bug 822094).
• The non-standardWindow.sizeToContent() method now clamps the minimal size: the window cannot be forced anymore to small sizes preventing the user from interacting with (Firefox bug 764240).
• Blend modes, such asoverlay,color-burn,hue, etc. have been added to the CanvasCanvasRenderingContext2D.globalCompositeOperation property (Firefox bug 748433).
• The prefixed version ofwindow.indexedDB —window.mozIndexedDB — was reintroduced to Gecko, so that bad cross-browser prefixing code (such asvar indexedDB = window.indexedDB || window.webkitIndexedDB …) doesn't break in Firefox. A better approach iswindow.indexedDB = window.indexedDB || window.webkitIndexedDB … (seeFirefox bug 770844.)

SVG

• The implementation of thecontentScriptType andcontentStyleType properties has been removed fromSVGSVGElement along with the removal from SVG2 (Firefox bug 819731).

MathML

• To help MathML authors debugging "invalid-markup" errors in their documents, MathML parsing errors (such as having too many / too few child elements) and warnings about deprecated attributes or wrong attribute values are now reported to the error console.
• Thescriptminsize attribute now accepts unitless values and percent values. They are interpreted as multiples of the default value (8pt).
• Unitless values are now also allowed for themathsize andfontsize attributes; they multiply the default value.

Changes for add-on and Mozilla developers

• ECMAScript for XML (E4X) is now fully disabled for all chrome and content scripts. It was previously disabled for content in Firefox 17 and has been removed entirely for Firefox 21. Use DOMParser/DOMSerializer or a non-native JXON algorithm instead.
• ThensIDOMParserJS interface no longer exists (Firefox bug 816410). SeensIDOMParser for alternatives.
• Content Preferences: ThensIContentPrefService interface is now deprecated and the asynchronousnsIContentPrefService2 storage API has been implemented.
• ThensIProfile andnsIProfileChangeStatus interfaces have been removed, along with other code supporting the pre-Firefox profile management system. You probably weren't using these interfaces, but if you were, you should stop doing so. This prevents defunct parts of the profile management system from vetoing the shutdown process.
• ThensIEventSource interface no longer exists (Firefox bug 819639).

See also

• Firefox 20 Release Notes
• Add-on Compatibility for Firefox 20