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Changes for Web developers
Quantum CSS enabled by default in Nightly
Firefox's new parallel CSS engine (also known as Stylo), part of Firefox Quantum, is newly-enabled by default in Firefox 57. 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.
standalonevalues of the
display-modemedia query are now supported (bug 1369815). See also the Web app manifest
- make grid-row-gap and grid-column-gap no longer be reset by the grid shorthand (bug 1387410).
Quantum CSS notes
- 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
gold(bug 1383323). Quantum fixes this bug.
- When you animate an offscreen element onscreen but specify a delay, Gecko does not repaint on some platforms, e.g. Windows (bug 1383239). This has been fixed in Quantum.
- In Gecko,
<details>elements can't be made open by default using the
openattribute if they have an
animationactive on them (bug 1382124). Quantum fixes this.
- In Gecko,
transitionswill not work when transitioning from a
text-shadowwith a color specified to a
text-shadowwithout a color specified (bug 726550). This has been fixed in Quantum.
- In Gecko, filling animations (e.g. with
animation-fill-mode: forwardsset) don't trigger transitions set on that same element when finished or cancelled (see bug 1192592 and these test cases for more information). This has been fixed in Quantum.
- 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). Quantum CSS fixes this.
- 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 is fixed in Firefox's new parallel CSS engine (also known as Quantum CSS or Stylo, planned for release in Firefox 57) (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). Quantum CSS fixes this.
- Gecko has a bug whereby length values are serialized into float values when converted into computed styles in the case of
stroke-dasharray. This has a few side effects, for example it may cause unexpected behaviour when animating these properties. Quantum CSS aims to fix this (bug 1379908).
- 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), including in media queries (bug 1390339). Gecko is not.
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).
- Data URLs are now treated as unique opaque origins, rather than inheriting the origin of the settings object responsible for the navigation (bug 1324406).
Removals from the web platform
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.
- Firefox 56 for developers
- Firefox 55 for developers
- Firefox 54 for developers
- Firefox 53 for developers
- Firefox 52 for developers
- Firefox 51 for developers
- Firefox 50 for developers
- Firefox 49 for developers
- Firefox 48 for developers
- Firefox 47 for developers
- Firefox 46 for developers
- Firefox 45 for developers
- Firefox 44 for developers
- Firefox 43 for developers
- Firefox 42 for developers
- 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