To test the latest developer features of Firefox,
install Firefox Developer Edition Firefox 42 was released on November 3, 2015. 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.
install Firefox Developer Edition Firefox 42 was released on November 3, 2015. 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
Highlights:
- Debugging Firefox for Android over Wifi
- Firefox OS Simulator configuration in WebIDE
- CSS filter presets
All devtools bugs fixed between Firefox 41 and Firefox 42.
CSS
- Vertical
writing-mode
is now supported with rtl scripts (bug 1131451). - The values of
caption-side
are now relative to the table, and changing actual meaning according to itswriting-mode
value bug 1202993. - Non-standard properties like
-moz-margin-start
are now aliases of their standard counterpart (margin-inline-start
, …). Previously, it was the opposite. This affects the value returned byCSSStyleDeclaration.cssText
and iteration of the properties in a style ruleand iteration of the properties in a style rule, that both use the canonical form (bug 1118103). - The prefixed version of CSS gradients can be turned off by setting the
layout.css.prefixes.gradients
preference tofalse
. - Several old bugs with
float
and margin collapsing behavior have been fixed (bug 478834, bug 538194, and bug 451791).
HTML
- Experimental support for the
referrer
attribute of the<img>
(bug 1166910),<iframe>
(bug 1175736),<a>
and<area>
(bug 1174913) has been added. There is no effect by default, thenetwork.http.enablePerElementReferrer
beingfalse
by default.
JavaScript
- The
Reflect
object has been implemented (bug 987514). - The implementation of the
Proxy
handler.ownKeys()
trap has been updated to match the final ES2015 specification (bug 1049662). - Calling
Map
,Set
, orWeakMap
withoutnew
, will now throw aTypeError
(bug 1083752).
Interfaces/APIs/DOM
DOM & HTML DOM
- Images with an
id
are no more listed as property of theWindow
interface:<img id="login">
isn't accessible aswindow.login
anymore. This behavior was introduced in Firefox 26 and has been removed to match a later change in the spec. (bug 959992) MouseEvent.offsetX
andMouseEvent.offsetY
have been added (bug 69787).- The
HTMLInputElement
interface has been experimentally extended to handle the upload of directories (bug 1164310). These four members can be exposed by setting thedom.input.dirpicker
preference totrue
: - The
Directory
interface has been experimentally extended (bug 1177688). The two membersDirectory.path
andDirectory.getContents
can be exposed by setting thedom.input.dirpicker
preference totrue
. - The
HTMLMediaElement.mozSrcObject
has been renamed inHTMLMediaElement.srcObject
(bug 1175523).
Service Workers
Request.context
has been removed (bug 1188062).- The Push API has been activated by default on Firefox for Desktop (bug 1153499), but only on the Nightly/Dev Edition/Beta channels. It is being deactivated by default in the Release channel until consumer UX and debugging features have been properly implemented (bug 1207875.) You can still activate it by enabling the
dom.push.enabled
pref in about:config. - The
PushManager.hasPermission()
method has been deprecated in the spec, and replaced with thePushManager.permissionState()
method. Firefox has updated its implementation to reflect this (bug 1183853.) - Service-worker-related additions to the Notifications API have been implemented (bug 1114554), but are disabled in this release.
Web Animations API
Our experimental implementation of Web Animations API have been extended to support:
- The
AnimationPlayer.playbackRate
property (bug 1127380). - The
CSSAnimation
andCSSTransition
interfaces (bug 1178186). - The
Animation.reverse()
method (bug 1150808). - The
AnimationPlaybackEvent
interface has been added andcancel
andfinish
are now fired onAnimation
(bug 1178664).
Web Components
Our experimental implementation of the Shadow DOM has been modified:
- When trying to invoke
Node.cloneNode()
on aShadowRoot
, throws aDataCloneError
exception (bug 1176757). - When invoking
Document.importNode()
with aShadowRoot
as an argument, we now throws aNotSupportedError
exception (bug 1177914). - When invoking
Document.adoptNode()
with aShadowRoot
as an argument, we now throws aHierarchyRequestError
exception (bug 1177991).
WebGL
- WebGL2
WebGLTransformFeedback
has been implemented (bug 1048724). - To obtain a WebGL2 context,
HTMLCanvasElement.getContext()
now takeswebgl2
instead ofexperimental-webgl2
(bug 1187174).
WebRTC
- The
RTCICECandidatePairStats.mozPriority
has been renamed toRTCICECandidatePairStats.priority
(bug 1184426).
New APIs
- The
ImageBitmap
interface and thecreateImageBitmap()
method have been implemented. They are available on regular window scripts and in Web workers and allow efficient posting of images between window and worker contexts (bug 1044102).
Miscellaneous
- The
IDBCursorWithValue
interface is now available in Web workers (bug 1188115). - Error events sent in Web workers doesn't bubble anymore (bug 1188141).
- Media Source Extensions (MSE) has been activated for all Web sites, and no more for a white list of sites (bug 1185611).
- The non-standard and deprecated
Window.mozRequestAnimationFrame()
has been removed (bug 909154). Use the standardWindow.requestAnimationFrame()
instead. - Speech synthesis (text-to-speech) has been implemented in Firefox Desktop for Windows, hidden behind the
media.webspeech.synth.enabled
flag inabout:config
(bug 1003457.) See Web Speech API for more information.
MathML
No change.
SVG
No change.
Audio/Video
No change.
HTTP
- Firefox 41 and earlier versions were incorrectly accepting undefined or invalid pseudo-header fields in HTTP/2 responses. This is now fixed and the only pseudo-header field accepted from Firefox 42 is the :status as per the specification. Response headers containing arbitrary fields are considered malformed. (bug 1136727)
Networking
- The CSP
upgrade-insecure-requests
directive has been implemented (bug 1139297).
Security
- EV certificates with a validity greater than 39 months are now considered and handled as DV certificates (bug 1145679).
Changes for add-on and Mozilla developers
Interfaces
nsIContentPolicy
- The
TYPE_EMBED
constant has been added tonsIContentPolicy
to allow Gecko internals and add-on code to better differentiate different types of requests. Previously,TYPE_OBJECT
was used for these cases (bug 1148030). - Similarly, the
TYPE_SUBDOCUMENT
constants has been split intoTYPE_FRAME
andTYPE_IFRAME
(bug 1148044).
XUL
No change.
JavaScript code modules
No change.
XPCOM
No change.
Other
No change.
See also
Older versions
- Firefox 41 for developers
- Firefox 40 for developers
- Firefox 39 for developers
- Firefox 38 for developers
- Firefox 37 for developers
- Firefox 36 for developers
- Firefox 35 for developers
- Firefox 34 for developers
- Firefox 33 for developers
- Firefox 32 for developers
- Firefox 31 for developers
- Firefox 30 for developers
- Firefox 29 for developers
- Firefox 28 for developers
- Firefox 27 for developers
- 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
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