Firefox 27 was released on February 4, 2014. This article lists key changes that are useful not only for web developers, but also Firefox and Gecko developers as well as add-on developers.

Changes for Web developers

Developer Tools

• Breakpoints can now be set on DOM events.
• JavaScript in the debugger panel can be unminified, using the { } button.
• The inspector now has an "edit-element-html" feature, without needing an add-on.
• Background-URLs and colors have preview in inspector. Even hovering over canvas elements will give a pop-up with an image preview.
• Reflow logging has been added.
• Styles of SVG elements are now inspectable (Firefox bug 921191).
• Failure to find the image when clicking URL link in CSS inspector has been fixed (Firefox bug 921686).
• TheX-SourceMap header is now supported (Firefox bug 765993).

More details inthis post.

CSS

• The-moz-grab and-moz-grabbing keywords on the CSScursor property have been unprefixed tograb andgrabbing (Firefox bug 880672).
• Support for the-moz-hsla() and-moz-rgba() functional notations has been dropped. Only the unprefixed versions,hsla() andrgba() are supported from now on (Firefox bug 893319).
• Thetrue value fortext-align has been added (Firefox bug 929991).
• Experimental support ofposition:sticky is now active by default on non-release builds (Firefox bug 902992). For releases builds, thelayout.css.sticky.enabled preference still needs to be set totrue.
• Theall shorthand property has been added (Firefox bug 842329).
• Theunset global value has been added; it allows to reset any CSS property (Firefox bug 921731).
• Curly braces are no longer allowed in HTMLstyle attributes: doing<div> was working in quirks mode, but won't anymoreFirefox bug 915053.
• Theoverflow property now works on<fieldset> (Firefox bug 261037).

HTML

• Thecolor value of the<input>type attribute has been implemented on desktop platforms. It was already available on mobile ones.
• Theallow-popups directive is now supported with thesandbox attribute of the<iframe> element (Firefox bug 766282).
• Blending of HTML elements using themix-blend-mode property has been implemented. Thelayout.css.mix-blend-mode.enabled preference must be set totrue (Firefox bug 902525).
• ThetypeMustMatch property of the<object> element is now supported (Firefox bug 827160).

JavaScript

ECMAScript 2015 implementation continues!

• Thespread operator is now supported in Function calls (Firefox bug 762363).
• The mathematical functionMath.hypot() has been implemented (Firefox bug 896264).
• Theyield* expression is now implemented (Firefox bug 666396).
• TheMapIterator,SetIterator andArrayIterator objects now match the specification (Firefox bug 881226).
• for...of loops now expect the ES2015 standarditerator protocol moving away from SpiderMonkey old iterator protocol usingStopIteration.
• String.match andString.replace now resetRegExp.lastIndex (Firefox bug 501739).

Interfaces/APIs/DOM

• Support for the twosetRange() methods on theHTMLInputElement interface has been added (Firefox bug 850364).
• Support for the twosetRange() methods on theHTMLTextAreaElement interface has been added (Firefox bug 918940).
• The methodsgetAllKeys() andopenKeyCursor() have been added toIDBObjectStore (Firefox bug 920633 andFirefox bug 920800).
• TheHTMLFormControlsCollection interface has been implemented (Firefox bug 913920).
• TheCanvasRenderingContext2D interface now supports the two methodsgetLineDash() andsetLineDash() and thelineDashOffset property (Firefox bug 768067).
• ThetypeMustMatch attribute has been implemented on theHTMLObjectElement interface (Firefox bug 827160).
• ThecopyFromChannel() andcopyToChannel() methods have been added toAudioBuffer (Firefox bug 915524).
• Event.isTrusted() is now unforgeable (Firefox bug 637248).
• The WebRTC API'sRTCIceCandidate object now includes atoJSON() method to help with signaling and debugging (Firefox bug 928304).
• TheNavigator.vibrate() method has been adapted to match the final specification: It now returnsfalse when the list is too long or has too large entries, instead of throwing (Firefox bug 884935).
• As part of the ongoing effort to standardize global objects, the non-standard stylesheet change event interfaces, includingStyleRuleChangeEvent,StyleSheetApplicableStateChangeEvent andStyleSheetChangeEvent, are no longer available from Web content. TheCSSGroupRuleRuleList interface, the implementation detail ofCSSRuleList, has also been removed (Firefox bug 872934 andFirefox bug 916871).
• Window.atob() now ignores whitespaces (Firefox bug 711180).
• WebGL:MOZ_ prefixed extension strings are deprecated. Support for them will be removed in the future. Use unprefixed extension string only. To get draft extensions, set thewebgl.enable-draft-extensions preferences (Firefox bug 924176).

MathML

No change.

SVG

• Blending of SVG elements using themix-blend-mode property has been implemented. Thelayout.css.mix-blend-mode.enabled preference must be set totrue (Firefox bug 902525).

Changes for addon and Mozilla developers

• Thedownloads-indicator button has gone away. You should now use thedownloads-button element. If you need to check that it has loaded its overlay, check for theindicator attribute on that button.
• Thechrome://browser/skin/downloads/indicator.css stylesheet is no longer referenced in Firefox.

Security

• TLS 1.2 has been implemented for improved security (Firefox bug 861266).

See also

• List of changes inMarionette for Firefox 27.