To test the latest developer features of Firefox,
install Firefox Developer Edition Firefox 48 was released on August 2, 2016. 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
- The position of elements can now be changed within the content (bug 1139187).
console.clear()to clear the console output (bug 659625).
- Added HTTP log inspection to the Web Console (bug 1211525).
- Added a Firebug theme (bug 1244054).
- Added the DOM Inspector (bug 1201475).
- Font inspector has been enabled by default again (bug 1280121).
- Improved suggestions for CSS properties (bug 1168246).
- Cookies, localstorage and sessionstorage entries are editable via double-click (bug 1231154, bug 1231179, bug 1231155).
<summary>elements have been activated by default on Nightly and Aurora (DevTools), but not on Beta or Release:
metaattributes now also supports the
origin-when-cross-originvalues (bug 1178337).
calc()has been improved to be closer to the specification:
- Our experimental implementation of CSS grids has been updated:
mask-modehas been added; the
autovalue has been renamed to
match-source, to match the spec (bug 1228354).
- Interpolation of
clip-pathbasic shapes in CSS animations and transitions is now supported (bug 1110460).
- Support for horizontal-in-vertical (tate-chu-yoko) text has been added via the
allvalue of the
text-combine-uprightproperty (bug 1097499).
- Support for the experimental
color-adjustproperty has been added, allowing pages to specify that background colors and images should be printed (bug 1209273).
::first-letterpseudo-element now also matches punctuation characters of type Pd that precede or immediately follow the actual first letter; this is a new requirement of CSS Pseudo-element module level 4 (bug 1260366).
-webkitprefixed properties and values have been added for web compatibility, behind the preference
layout.css.prefixes.webkit, defaulting to
-webkit-background-clip(as background-clip) text value (bug 759568).
- The value
-webkit-inline-boxis now an alias of
displayproperty. (bug 1257661).
-webkit-align-contentwere added as aliases for the unprefixed properties and the values
displayproperty as aliases for the unprefixed values (bug 1274096).
displayas aliases for modern CSS Flexbox (bug 1208635).
background-clipis now available in all type of Firefox (and not only non-release builds) (bug 1263516).
positionpropertis on the top layer element (bug 1236828).
- Added an internal-only syntax for
@supportsto detect pref (bug 1259889).
String.prototype.padEnd()methods have been implemented (bug 1260509).
- The ES2015
Array.prototype[@@unscopables]properties have been implemented (bug 1054759 and bug 1258163).
- The ES2015
Symbol.isConcatSpreadablesymbol has been implemented (bug 1041586).
- The ES2015
Array[@@species]getter has been implemented (bug 1165052).
- The ES2015
%TypedArray%[@@species]getter have been implemented (bug 1165053).
Intl.getCanonicalLocales()method of the ECMAScript Internationalization API draft has been implemented (bug 1263040).
Deprecations and removals
- The deprecated old Proxy API (
Proxy.createFunction()) has been removed. Use the standard
Proxyobject instead (bug 892903).
String.prototype.contains()method has been removed (it was deprecated since version 40). Use the
String.prototype.includes()method instead (bug 1103588).
- The non-standard
RegExp.prototype.multiline) has been removed. Use the standard m flag instead (bug 1219757).
__defineSetter__methods can no longer be called at the global scope without any object. (bug 1253016).
DOM & HTML DOM
- Dropped the "Moz" prefix from the
CSSKeyframesRuleinterfaces (bug 1256178).
NavigatorConcurrentHardwaremixin has been implemented, which adds the
window.navigator.hardwareConcurrencyproperty to the
Navigatorinterface. This lets Web sites and apps get at least an approximation of how many processing cores are available to run
Workers in (bug 1008453).
Node.isSameNode()method, which was removed in Firefox 10, has returned after being added back into the specification after a lengthy absence (bug 1256299).
- Firefox now returns proper exceptions instead of numbers when things go wrong during a call to
Element.animate()is now activated by default (bug 1245000).
- The two methods
Element.insertAdjacentElement()have been implemented (bug 811259).
Document.scrollingElementgot enabled by default (bug 1265032).
Node.prefixwere moved to the
AttrAPIs (bug 1055776).
- Per the latest specification, the values of
KeyboardEvent.codereturned for the following keys have been changed see (bug 1264150):
"IntlHash"has been removed.
- All keys whose
codevalues were reported as "" in earlier versions of F9irefox are now reported as "Unidentified".
- The two methods
MediaStreamTrack.clone()have been implemented (bug 1208371).
iceRestartentry is now supported in the
createOffer()to be used to request ICE restarts (bug 906986).
RTCPeerConnection.createOffer()method now prefers the VP9 video codec by default; previously VP8 was preferred (bug 1242324.
- WebM/VP8 video that includes video resolution changes that has been recorded using
MediaRecordercan now be played back successfully.
- The Web Crypto API is now available in Web workers (bug 842818).
CustomEventinterface is now available in Web Workers (bug 1003432).
DOMApplicationsManager.getNotInstalled()method has been removed (bug 1255036).
- Several Firefox OS APIs that were erroneously exposed to the Web have now been hidden as they should have been —
MozSettingsEvent(see bug 1043562, bug 1256414, and bug 1256046).
- Support for UTF-16 has been removed from
RTCStatsReportis now a true
maplikeinterface: in addition to
has(), the methods
keys(), as well as the
sizegetter have been implemented (bug 906986).
Request.cacheproperty has been added allowing to control the cache behavior (bug 1120715).
- Handling of dead keys on Mac OS X has been changed to work the same as other platforms; they no longer fire a
keypressevent when no text is generated when the focused element isn't editable (when the focused element is editable, dead key causes composition events instead of keyboard events on Mac OS X). Also, like on other platforms, the value of
"Dead"for dead keypresses which don't generate text in other situations.
- Support for the
Upgrade-Insecure-Requestsheader has been added (bug 1243586).
block-all-mixed-contentCSP directive has been implemented (bug 1122236)
Changes for add-on and Mozilla developers
- The Social Worker API has been removed.
- Added the
@supportsfunction to allow hiding portions of chrome stylesheets behind boolean preferences. (bug 1259889)
- Firefox 47 for developers
- Firefox 46 for developers
- Firefox 45 for developers
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