Firefox 27 for developers
=========================

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).
* The `X-SourceMap` header is now supported (Firefox bug 765993).

More details in this post.

### CSS

* The `-moz-grab` and `-moz-grabbing` keywords on the CSS `cursor` property have been unprefixed to `grab` and `grabbing` (Firefox bug 880672).
* Support for the `-moz-hsla()` and `-moz-rgba()` functional notations has been dropped. Only the unprefixed versions, `hsla()` and `rgba()` are supported from now on (Firefox bug 893319).
* The "`true`" value for `text-align` has been added (Firefox bug 929991).
* Experimental support of `position:sticky` is now active by default on non-release builds (Firefox bug 902992). For releases builds, the `layout.css.sticky.enabled` preference still needs to be set to `true`.
* The `all` shorthand property has been added (Firefox bug 842329).
* The `unset` global value has been added; it allows to reset any CSS property (Firefox bug 921731).
* Curly braces are no longer allowed in HTML `style` attributes: doing `<div style="{ display: none }">` was working in quirks mode, but won't anymore Firefox bug 915053.
* The `overflow` property now works on `<fieldset>` (Firefox bug 261037).
### HTML

* The `color` value of the `<input>` `type` attribute has been implemented on desktop platforms. It was already available on mobile ones.
* The `allow-popups` directive is now supported with the `sandbox` attribute of the `<iframe>` element (Firefox bug 766282).
* Blending of HTML elements using the `mix-blend-mode` property has been implemented. The `layout.css.mix-blend-mode.enabled` preference must be set to `true` (Firefox bug 902525).
* The `typeMustMatch` property of the `<object>` element is now supported (Firefox bug 827160).
### JavaScript

ECMAScript 2015 implementation continues!

* The spread operator is now supported in Function calls (Firefox bug 762363).
* The mathematical function `Math.hypot()` has been implemented (Firefox bug 896264).
* The `yield*` expression is now implemented (Firefox bug 666396).
* The `MapIterator`, `SetIterator` and `ArrayIterator` objects now match the specification (Firefox bug 881226).
* for...of loops now expect the ES2015 standard iterator protocol moving away from SpiderMonkey old iterator protocol using `StopIteration`.
* `String.match` and `String.replace` now reset `RegExp.lastIndex` (Firefox bug 501739).
### Interfaces/APIs/DOM

* Support for the two `setRange()` methods on the `HTMLInputElement` interface has been added (Firefox bug 850364).
* Support for the two `setRange()` methods on the `HTMLTextAreaElement` interface has been added (Firefox bug 918940).
* The methods `getAllKeys()` and `openKeyCursor()` have been added to `IDBObjectStore` (Firefox bug 920633 and Firefox bug 920800).
* The `HTMLFormControlsCollection` interface has been implemented (Firefox bug 913920).
* The `CanvasRenderingContext2D` interface now supports the two methods `getLineDash()` and `setLineDash()` and the `lineDashOffset` property (Firefox bug 768067).
* The `typeMustMatch` attribute has been implemented on the `HTMLObjectElement` interface (Firefox bug 827160).
* The `copyFromChannel()` and `copyToChannel()` methods have been added to `AudioBuffer` (Firefox bug 915524).
* `Event.isTrusted()` is now unforgeable (Firefox bug 637248).
* The WebRTC API's `RTCIceCandidate` object now includes a `toJSON()` method to help with signaling and debugging (Firefox bug 928304).
* The `Navigator.vibrate()` method has been adapted to match the final specification: It now returns `false` 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, including `StyleRuleChangeEvent`, `StyleSheetApplicableStateChangeEvent` and `StyleSheetChangeEvent`, are no longer available from Web content. The `CSSGroupRuleRuleList` interface, the implementation detail of `CSSRuleList`, has also been removed (Firefox bug 872934 and Firefox bug 916871).
* `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 the `webgl.enable-draft-extensions` preferences (Firefox bug 924176).
### MathML

*No change.*

### SVG

* Blending of SVG elements using the `mix-blend-mode` property has been implemented. The `layout.css.mix-blend-mode.enabled` preference must be set to `true` (Firefox bug 902525).
Changes for addon and Mozilla developers
----------------------------------------

* The `downloads-indicator` button has gone away. You should now use the `downloads-button` element. If you need to check that it has loaded its overlay, check for the `indicator` attribute on that button.
* The `chrome://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 in Marionette for Firefox 27.
### Older versions

* Firefox 26 for developers
* Firefox 25 for developers
* Firefox 24 for developers
* Firefox 23 for developers
* Firefox 22 for developers
* Firefox 21 for developers
* Firefox 20 for developers
* Firefox 19 for developers
* Firefox 18 for developers
* Firefox 17 for developers
* Firefox 16 for developers
* Firefox 15 for developers
* Firefox 14 for developers
* Firefox 13 for developers
* Firefox 12 for developers
* Firefox 11 for developers
* Firefox 10 for developers
* Firefox 9 for developers
* Firefox 8 for developers
* Firefox 7 for developers
* Firefox 6 for developers
* Firefox 5 for developers
* Firefox 4 for developers
* Firefox 3.6 for developers
* Firefox 3.5 for developers
* Firefox 3 for developers
* Firefox 2 for developers
* Firefox 1.5 for developers