Firefox 28 for developers

• The console.exception property has been added (Firefox bug 922214).
• The console.assert() property has been added (Firefox 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: 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.

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

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

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

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

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

No change.

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

• Support of SPDY/2 has been removed.

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

• CSP was not enforced in sandboxed iframes. This has been fixed (Firefox 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 (Firefox bug 855326).