Firefox 28 for developers

Firefox 28 was released on March 18, 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

• The console.exception property has been added (bug 922214).
• The console.assert property has been added (bug 760193).
• App Manager: a new Manifest Editor was added.
• App Manager: the toolbox used for debugging apps is now embedded in the app manager UI.
• Web Console: added a "split console" mode - press Escape to quickly open the console in any other tool.
• Web Console: added a dark theme for the output.
• Debugger: pretty-print minified JavaScript.
• Debugger: simply hover over any variable or click on it to bring up a pop-up that displays the current value.
• Inspector: added a color picker in rules view and various tooltips.
• Browser Toolbox: allows add-on and platform developers to use almost all of the developer tools while targeting the browser itself.

More details in this post.

CSS

• Support for multi-line flexbox has been added (bug 939901).
• Longhand East Asian counter styles have been implemented (bug 934072).
• Experimental support for the background-blend-mode property has been added, but is disabled by default (bug 841601).
• The none value has been added to font-variant-ligatures (bug 913264).
• Support for the :hover user action pseudo-class on pseudo-elements has been implemented (bug 922669).

HTML

• <input type=color> and <input type=number> have been implemented, disabled by default.

JavaScript

• ECMAScript 2015 implementation continues:
  • New Array methods have been implemented: Array.prototype.entries() and Array.prototype.keys() (bug 894658).
• A bug causing that Object.getOwnPropertyNames() did not see unresolved properties of Error objects has been fixed (bug 724768).

Interfaces/APIs/DOM

• HTMLVideoElement.canPlayType('video/webm') now reports maybe. (bug 884275).
• The DocumentFragment.getElementById() method has been implemented. E.g. document.createDocumentFragment().getElementById() (bug 933193).
• The KeyboardEvent.repeat attribute has been implemented (bug 600117).
• The File constructor, e.g. new File(["foo"], "foo.txt") has been implemented. (bug 819900).
• The navigator.plugins is no more enumerable, for privacy reasons (bug 757726).
• The two attributes Window.screenX and Window.screenY now return CSS pixels (and no more device pixels) (bug 943668).
• The two methods CanvasRenderingContext2D.drawSystemFocusRing() and CanvasRenderingContext2D.drawCustomFocusRing() have been implemented. The preference canvas.focusring.enabled must be set to true to activate both (bug 540456).
• The willReadFrequently context attribute for "2d" canvas contexts has been implemented (see HTMLCanvasElement.getContext()) (bug 884226).
• The following attributes and methods of NavigatorID have been implemented on WorkerNavigator to allow their use in workers: appCodeName, product, and taintEnabled() (bug 925847).
• The previousElementSibling and {domxref("NonDocumentTypeChildNode.nextElementSibling" , "nextElementSibling")}} properties has been removed from DocumentType, because of compatibility problems (bug 932501).

MathML

• Support of the mathvariant attribute has been added (bug 114365).

SVG

No change.

Audio/Video

• Opus in WebM is now supported (bug 887978).
• The VP9 video decoder is now supported (bug 833023).

Network

• Support of SPDY/2 has been removed.

Changes for addon and Mozilla developers

• The interface of DeferredTask.jsm has been changed, and the isPending(), start(), flush(), and cancel() methods have been removed (bug 940408).

Security

• CSP was not enforced in sandboxed iframes. This has been fixed (bug 886164).
• The CSP 1.1 experimental script-nonce directive has been implemented. The preference security.csp.experimentalEnabled should be set to true to enable this functionality (bug 855326).

See also

• Site Compatibility for Firefox 28

Older versions