Firefox 18 for developers
=========================

Firefox 18 was released on January 8, 2013. 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
--------------------------

### HTML

* The `reversed` attribute of the `<ol>` element is now supported (Firefox bug 601912).
* The `crossorigin` attribute of the `<link>` element is now supported (Firefox bug 786564).
* The `allowfullscreen` attribute of the `<iframe>` has been implemented and it's prefixed predecessor `mozallowfullscreen` is now deprecated.
### CSS

* The `min-width` and `min-height` now uses the `auto` keyword as *initial value* (This has an effect only on flex items as it resolves to `0`, the previous initial value, for other items). (Firefox bug 763689)
* The cascade has been updated: now author `!important` rules override CSS animations. (Firefox bug 783714)
* The `background` shorthand property now recognizes CSS3 `background-size` property specified inside. (Firefox bug 570326)
* Initial support for the CSS Flexbox Module has been landed. It is disabled by default but can be enabled by setting `layout.css.flexbox.enabled` to true (Firefox bug 666041).
### DOM/APIs

* `navigator.mozPay` has been landed. (Firefox bug 767818)
* `window.devicePixelRatio` has been landed. (Firefox bug 564815)
* The MacOS X backend for `window.navigator.battery` has been implemented. (Firefox bug 696045)
* `MozBlobBuilder` is removed. Developers need to use `Blob` constructor for creating a `Blob` object. (Firefox bug 744907)
* The `visibilitychange` event and the Page Visibility API has been unprefixed (Firefox bug 812086).
* `TextDecoder` and `TextEncoder` have been added. Note that the implementation and spec of these evolved and have been changed in Firefox 19 (Firefox bug 764234).
* `HTMLMediaElement.src` has been separate in two properties: the standard `src` property, dealing with strings, and the prefixed `mozSrcObject` property, dealing with media streams (Firefox bug 792665).
* Support for transferable objects.
* The `Screen.lockOrientation()` method now supports an `Array` of strings as argument (Firefox bug 784549.
### JavaScript

* Harmony's (ECMAScript 2015) Direct Proxies have been landed (Firefox bug 703537). Warning: the implementation contains a couple of known bugs, missing features and misalignments with the current state of the spec. Do not rely on it for production code.
* The ECMAScript 2015 `contains()` method is now implemented on strings. This is unfortunately not compatible with Mootools 1.2, which expects different behavior from `contains()` on strings but does not ensure it. Newer versions of Mootools fix this issue; sites should upgrade their Mootools version to something newer than 1.2.
### WebGL

* The prefixed version of the `EXT_texture_filter_anisotropic` WebGL extension, "MOZ\_EXT\_texture\_filter\_anisotropic" has been removed (Firefox bug 790946).
### SVG

### MathML

### XUL

### Network

* Quality factors ("q-values") are now clamped to 2 digits (e.g. in HTTP `Accept-Language` headers) (Firefox bug 672448).
* The `ALLOW-FROM` syntax of the `X-FRAME-OPTIONS` HTTP Response header is now supported (Firefox bug 690168).
### Developer tools

Changes for add-on and Mozilla developers
-----------------------------------------

### Interface changes

`nsIStreamListener`

The 4th parameter (aOffset) of `onDataAvailable()` method changes to unsigned long long. (Firefox bug 784912)

`nsIUploadChannel`

`setUploadStream()` supports over 2GB content-length (Firefox bug 790617)

`nsIEditor`

`addEditorObserver()` has been removed, use `setEditorObserver()` instead, `removeEditorObserver()` no longer takes a `nsIEditorObserver` parameter (Firefox bug 785091)

`nsIHttpProtocolHandler`

`http-on-modify-request` observers are no longer guaranteed to be called synchronously during `nsIChannel.asyncOpen()`.
 For observers that need to be called during `asyncOpen()`, the new `http-on-opening-request` observer topic has been added. `See` (Firefox bug 800799)


`nsIProtocolProxyService`

The `resolve` method has been removed. Now, only the `asyncResolve` method can be used. See (Firefox bug 769764)

#### New interfaces

#### Removed interfaces

The following interfaces have been removed.

* `nsIEditorObserver`
See also
--------

* Firefox 18 Beta Release Notes
* Aurora 18: HiDPI & Touch Events (Mozilla Hacks)
* Add-on Compatibility for Firefox 18 (Add-ons Blog)
### Older versions

* 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