Firefox 29 for developers

Firefox 29 was released on April 29, 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

Major changes include:

Vastly improved web console - Arrays are shown inline without clicking to bring up in the right inspector, window objects show their url, etc.
Added the console API to Web Workers (bug 620935). Now you can log messages to the Web Console from Web Workers.
The Network Monitor tool now shows performance statistics using pie charts (bug 846599).
On the Inspector, preview tooltips of CSS transforms are now available (bug 726427).
DOM elements seen in the debugger and console can be removed or inspected directly, via the new buttons to the right of the variable listing.
A CSS source map is now supported by the Style Editor (bug 926014).
Autocompletion of CSS properties and values has been added to the Style Editor (bug 717369).

See the Mozilla Hacks blog post for details and other smaller changes.

CSS

CSS variables have been implemented (bug 773296). Mozilla Hacks article can be found here. They are enabled by default only for non-release builds (on release builds flip the pref layout.css.variables.enabled to true if you want to play with them).
Flexboxes now support visibility: collapse (bug 783470).
The box-sizing property has been unprefixed (bug 243412).
The will-change property, a hint to that something will animate has been added. The preference layout.css.will-change.enabled must be switched to true to enable it. (bug 940842)
Scientific exponential notation, like 3e1 or 10e+0, is now supported for <number> values and derivatives, like <percentage> and unit values, but not <integer> (bug 964529).
Images of type <gradient> are now supported in border-image (bug 709587).
The touch-action property has been implemented. It is not activated by default; the layout.css.touch_action.enabled pref controls it. (bug 795567)
Remove redundant default style for <pre> element from quirk.css (bug 948914).
CSS Variables fallback incorrectly implemented (primary cycles) (bug 950497).
@supports conditions with tokens after a declaration's priority should evaluate to false (bug 909170).

HTML

<input type=color> and <input type=number> are available by default.
Support for the non standard <pre cols> has been removed, as well as the layout effect of <pre wrap> . Both effects can, and should, be achieved using CSS. (bug 949879)

JavaScript

New ECMAScript 2015 String methods: String.prototype.codePointAt() and String.prototype.fromCodePoint() have been implemented (bug 918879).
The ECMAScript Internationalization API (ECMA-402) has been implemented and is now enabled by default in Firefox Desktop (bug 853301):
- New objects in the new Intl object namespace:
- The following methods of String, Number and Date have been updated to include the locales and options arguments per ECMA-402:
To match the updated ECMAScript 2015 draft specification, the Map and Set objects now treat -0 and +0 as the same when checking for key and value equality.
Promise has been enabled by default (bug 918806).
Completed generators now return an IteratorResult object instead of throwing (bug 958951).
A malformed JSON string parsed by JSON.parse() now yields a more detailed error message containing the line and column number that caused the parsing error. This is useful when debugging large JSON data.
The ArrayBuffer.isView() method has been added (bug 896105).

Interfaces/APIs/DOM

A new type of workers, SharedWorker, is now available by default (bug 924089).
The URLUtils interface now supports the searchParams property returning a URLSearchParams object, allowing to modify the search params of an URL (bug 887836). The URLSearchParams constructor allows easier parsing of query strings.
The NavigatorOnLine.onLine property is now supported on WorkerNavigator , allowing to know the online/offline status in workers (bug 925437).
As part of the implementation of Web Components, the HTMLShadowElement interface has been implemented behind the dom.webcomponents.enabled. Flip it to true if you want to use it. (bug 887538).
The read-only property HTMLIFrameElement.sandbox is no longer a string but an HTMLSettableToken (bug 845057).
On HTMLCanvasElement.getContext(), the value moz-webgl is no longer supported. Use the standard webgl value (bug 913597).
The constructor for ImageData has been added. This interface can be used in a Worker. (bug 959958)
The property location.origin is now available in workers (via WorkerLocation) (bug 964148).
The ValidityState.badInput property has been implemented (bug 827161).
The deprecated Window.pkcs11 property has been removed; it was returning null since Firefox 3.0.14. (bug 964964)
The Node.cloneNode() and Document.importNode() methods take the Boolean deep argument. Until now, if omitted, these methods acted as if the value of deep was true. But this behavior has been changed as per the latest spec, and if omitted, the methods will act as if the value was false. (bug 937461)
Window._content is no longer available to Web content (bug 946564).
URLUtils.port behavior has been slightly changed: set to '' will set it to the default port associated with the protocol, and 0 to 0. (bug 930450)
Document.referrer is now based on the incumbent script (bug 887928).
The Gamepad API is enabled by default (bug 878828).
The CanvasRenderingContext2D.drawSystemFocusRing() method got renamed to CanvasRenderingContext2D.drawFocusIfNeeded() (bug 959820).

MathML

No change.

SVG

No change.

Security

The CSP 1.1 experimental hash-source directive has been implemented. The preference security.csp.experimentalEnabled should be set to true to enable this functionality (bug 883975).

Changes for add-on and Mozilla developers

Australis and add-on compatibility - This is a major Firefox theme change that affects most extensions that involving the Firefox user interface.
nsISecurityCheckedComponent has been removed (bug 794943). Most consumers can simply remove nsISecurityCheckedComponent from their interface definition and they will continue to work.

Non-Australis changes TBD.