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This article provides information about the changes in Firefox 57 (a.k.a. Firefox Quantum) that will affect developers. Firefox 57 was released on November 14, 2017.
Firefox 57 === Firefox Quantum
Firefox 57 has been given the release name Quantum, after the Firefox Quantum engineering project that has aimed to rebuild Firefox from the ground up, bringing with it major performance, stability, and visual improvements. This is the first version of Firefox to ship some of these improvements, so we wanted to mark the occasion.
Note: To read more about the Quantum features in this release, see Firefox Quantum Developer Edition: the fastest Firefox ever with Photon UI and better tooling by Dan Callahan.
Firefox's new parallel CSS engine — also known as Quantum CSS or Stylo — is enabled by default in Firefox 57 for desktop, with Mobile versions of Firefox to follow later on. Developers shouldn't notice anything significantly different, aside from a whole host of performance improvements. There are however a number of minor functional differences in Stylo, implemented to fix non-standard Gecko behavior that should be eliminated. We will report on such differences on reference pages and in the release notes as appropriate (see Quantum CSS notes).
Changes for Web developers
standalonevalues of the
display-modemedia query are now supported (bug 1369815). See also the Web app manifest
grid-column-gapproperties are no longer reset by the
gridshorthand (bug 1387410).
layout.css.clip-path-shapes.enabledpreference has been removed (bug 1399767). This preference allowed disabling the
clip-path. This support was shipped in Firefox 54 and can no longer be disabled.
Quantum CSS notes
Following bugs have been fixed in Quantum:
- Radial gradient values like
radial-gradient(circle gold,red)will work in the old Gecko style system, even though they shouldn't because of the missing comma between
- When you animate an offscreen element onscreen but specify a delay, Gecko does not repaint on some platforms, e.g. Windows (bug 1383239).
- In Gecko,
<details>elements can't be made open by default using the
openattribute if they have an
animationactive on them (bug 1382124).
- In Gecko,
transitionswill not work when transitioning from a
text-shadowwith a color specified to a
text-shadowwithout a color specified (bug 726550).
- In Gecko, cancelling a filling animation (e.g. with
animation-fill-mode: forwardsset) can trigger a transition set on the same element, although only once (see bug 1192592 and these test cases for more information). In general declarative animations should not trigger transitions.
- Animations using em units are not affected by changes to the
font-sizeon the animated element's parent in Gecko, whereas they should be (bug 1254424).
- Gecko also deals with
font-sizeinheritance differently from Quantum CSS, meaning that for some language settings inherited font sizes end up being smaller than expected (see bug 1391341).
- Gecko reuses the same mechanism used when parsing a url-token when parsing the
url-prefix()URL matching functions for a
@-moz-documentrule. Quantum CSS does not use the same mechanism and it does not consider tokens invalid when they contain brackets or quotes (bug 1362333).
- In Gecko, when you set a system font as the value of a canvas 2D context's
menu), getting the font value fails to return the expected font (it returns nothing). This has been fixed in Quantum. (bug 1374885).
- In Gecko, when you create a detached subtree (e.g. a
createElement()that is not yet inserted into the DOM), the subtree's root element is set as a block-level element. In Quantum CSS this is set as inline, as per spec (bug 1374994).
- In Gecko,
calc()expressions are rejected — causing the value to be invalid — when used as the radius component of a
radial-gradient()function (bug 1376019).
- In Gecko,
calc(1*2*3)is not parsed successfully; Quantum CSS fixes this (bug 1379467).
- In Quantum CSS,
calc()is supported everywhere that the spec explains it should be (bug 1350857). In Gecko it is not.
- Gecko has a bug whereby the
::afterpseudo-elements are still generated even if the
contentproperty value is set to
none. As per spec, they shouldn't be (bug 1387931).
- Another Gecko bug means that the
background-positionproperty can't be transitioned between two values containing different numbers of
<position>values, for example
background-position: 10px 10px;and
background-position: 20px 20px, 30px 30px;(see bug 1390446).
- The non-standard
for each...in(E4X) loop has been removed. Please use
unwatch()methods are deprecated, will now throw a warning when used, and will be removed soon (bug 934669).
- The non-standard
StopIterationobjects as well as the legacy iteration protocol have been removed (bug 1098412).
- Async generator is now enabled (bug 1352312).
- for await (... of ...) syntax is now enabled (bug 1352312).
PerformanceObserverAPI is now enabled by default (bug 1386021).
AbortSignalinterfaces (known as the Abort API) have been added, allowing DOM requests (such as fetch requests) to be aborted if desired (bug 1378342).
-  The Storage API is implemented and enabled by default (bug 1399038).
Selection.typeproperty of the Selection API is now implemented (bug 1359157).
Document.createEvent('FocusEvent')is now supported (bug 1388069).
filesproperty of the
HTMLInputElementinterface is now settable (bug 1384030).
HTMLDocument.getSelection()method has been moved to the
Documentinterface so it is available to XML documents (bug 718711).
messageerrorevent is now implemented, and can have code run in response to it firing via event handlers implemented on message targets — see
Headersvalues are iterated over, they are automatically sorted in lexicographical order, and values from duplicate header names are combined (bug 1396848).
Media and WebRTC
- Support for messages of arbitrary size (up to 1GiB, although 256kiB is more interoperable) is now supported on
RTCDataChannelthrough use of the end-of-record (EOR) flag on SCTP messages. See Understanding message size limits in Using WebRTC data channels for more information (bug 979417).Because Firefox doesn't yet support the SCTP ndata protocol that provides the ability to interleave SCTP messages from multiple sources, sending large data objects can cause significant delays on all other SCTP traffic. See bug 1381145 to track progress on implementing and deploying ndata support in Firefox..
RTCDataChannel.send()method can now throw a
TypeErrorexception if the size of the message you're trying to send is not compatible with the receiving user agent (this is implemented as part of bug 979417).
- The MediaStream Recording API has been updated so that
errorevents sent to report problems that occur while recording are now of type
MediaRecorderErrorEventrather than being generic events.
- Updated the documentation around
OfflineAudioContextsince its constructor's inputs can now be specified in an object rather than as a list of parameters (bug 1388591).
- The Web Audio API now properly supports multi-channel output (bug 1378070).
resource://URLs no longer leak information (bug 863246)
- Data URIs are now treated as unique opaque origins, rather than inheriting the origin of the settings object responsible for the navigation (bug 1324406).
- Firefox headless mode now includes a
-screenshotflag that allows you to take website screenshots directly from the command line (bug 1378010).
Removals from the web platform
<link rel="preload">(see Preloading content with rel="preload") has been disabled in Firefox 57 because of various web compatibility issues (e.g. bug 1405761). An improved version that works for non-cacheable resources is expected to land in Firefox 58.
Changes for add-on and Mozilla developers
Starting in Firefox 57, all support for XPCOM-based add-ons has been removed. All extensions must be converted into the new browser extensions (also known as WebExtensions) or they will not work.
The following APIs have been added or extended:
- support for separators through
- support for separators through
theme_iconsproperty for light/dark theme icons
FindProxyForURL()can now return an object
runtime.openOptionsPage()support on Android
- Firefox 56 for developers
- Firefox 55 for developers
- Firefox 54 for developers
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