Firefox 38 was released on May 12th, 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:

• Bypass audio nodes in Web Audio Editor
• "copy" command in Web Console
• Highlight and filter XmlHttpRequests in Web Console
• See optimized-out variables in the Debugger
• See security warnings in the Network Monitor
• See transferred sizes in the Network Monitor
• Play/pause all animations in the page

All devtools bugs fixed between Firefox 37 and Firefox 38.

CSS

• Support forruby-position andruby-align have been added and is available by default (Firefox bug 1055676Firefox bug 1123917 andFirefox bug 1039006).

• The:unresolved pseudo-class has been implemented for custom elements (Firefox bug 1111633).

• The predefined styleethiopic-numeric now uses a space, instead of a dot, as the suffix to match a recent change to the spec (Firefox bug 1120721).

• CSS transitions on generated content (with::before and::after) on both an inline and the block that splits them now start as expected by the specification (Firefox bug 1110277).

• The implementation of CSS Logical Properties made big progress. The following properties are available behind thelayout.css.vertical-text.enabled flag (false by default):

  • Direction-independent equivalents ofwidth andheight:block-size andinline-size (Firefox bug 1117983).
  • Direction-independent equivalents ofmin-width andmin-height:min-block-size andmin-inline-size (Firefox bug 1117983).
  • Direction-independent equivalents ofmax-width andmax-height:max-block-size andmax-block-size (Firefox bug 1117983).
  • Direction-independent equivalents ofmargin-top,margin-right,margin-bottom andmargin-left:margin-block-start,margin-block-end,margin-inline-start andmargin-inline-end (Firefox bug 649142).
  • Direction-independent equivalents ofpadding-top,padding-right,padding-bottom andpadding-left:padding-block-start,padding-block-end,padding-inline-start andpadding-inline-end (Firefox bug 649142).
  • Direction-independent equivalents ofborder-top,border-right,border-bottom andborder-left and their longhands for width, style and color:border-block-start,border-block-start-width,border-block-start-style,border-block-start-color,border-block-end,border-block-end-width,border-block-end-style,border-block-end-color,border-inline-start,border-inline-start-width,border-inline-start-style,border-inline-start-color,border-inline-end,border-inline-end-width,border-inline-end-style andborder-inline-end-color (Firefox bug 649142).
  • Direction-independent equivalents oftop,right,bottom andleft:inset-block-start,offset-block-end,offset-inline-start andoffset-inline-end (Firefox bug 1120283).

• HowCSS transitions start has been modified to match a recent change of the specifications, aiming at having an interoperable behavior between browsers (Firefox bug 960465).

HTML

• The<label> element no longer dispatches events to the label target element if interactive content is found between the event target and the label (Firefox bug 229925).
• The<picture> element has been activated by default (Firefox bug 1017875).
• The<meta name="referrer"> is supported for navigations from the context menu or via a middle-click (Firefox bug 1113431).

JavaScript

• Generator.prototype.return() is implemented (Firefox bug 1115868).

• Setter with arest parameter is now aSyntaxError (Firefox bug 1089632).

• Thename property of functions is configurable now (Firefox bug 1084019).

• SeveralArray methods have been implemented fortyped arrays as well:

  • Theof() andfrom() methods (Firefox bug 896608).
  • TheforEach() method (Firefox bug 1107645).
  • Thefilter() andmap() methods (Firefox bug 1121936).
  • Theslice() method (Firefox bug 1121935).

• Duplicated parameter name is no longer allowed when rest-parameter is present (Firefox bug 1096376).

• Duplicated parameter name is no longer allowed in arrow functions (Firefox bug 1096377).

• Duplicated parameter name is no longer allowed in concise method definitions (Firefox bug 1096378).

• Warning is shown whenMap/Set/WeakMap constructor is called withoutnew (Firefox bug 1108930).

• Theget,has, anddelete methods ofWeakMap objects no longer throw when thekey parameter is not an object (Firefox bug 1127827).

• The optional and non-standard secondfallback parameter forWeakMap.prototype.get() has been removed (Firefox bug 1127827).

• When defining agenerator method,set andget are no longer invalid names (Firefox bug 1073809).

• RegExp.prototype.source now returns "(?:)" instead of an empty string for empty regular expressions (Firefox bug 1130798).

• RegExp.prototype.source andRegExp.prototype.toString() now escape regular expression patterns properly (e.g., line terminators, "\n") (Firefox bug 1130860).

• TheRegexpglobal,ignoreCase,multiline, andsticky properties are now prototype accessor properties rather than own data properties ofRegExp instances (Firefox bug 1120169).

• TheRegExp.prototype.source property is now prototype accessor property rather than own data property ofRegExp instances (Firefox bug 1120169). Available only in non-Release version, due toFirefox bug 1150297.

• Function.prototype.toString() now throws forProxy objects (Firefox bug 1100936).

Interfaces/APIs/DOM

• The Fetch APIfetch() method has been implemented (Firefox bug 1039846).
• BroadcastChannel API has been implemented and is available inWeb Workers (Firefox bug 966439 andFirefox bug 1121420).
• The Console API is now available inWeb Workers.
• CanvasRenderingContext2D.clearHitRegions() has been implemented (Firefox bug 1119527).
• Constants ofKeyboardEvent.location,DOM_KEY_LOCATION_MOBILE and DOM_KEY_LOCATION_JOYSTICK, have been removed, since they were removed from the DOM Level 3 Spec (Firefox bug 936313.
• KeyboardEvent.code is now available; previously it was only available in prerelease builds. (Firefox bug 1126673)
• KeyboardEvent.code now supports special keys on Sun keyboards on Linux, Android, and Firefox OS. (Firefox bug 1020139)
• TheTextEncoder() constructor has been changed to match the spec: when an invalid parameter is passed, theRangeErrorDOMException is now raised, rather than the erroneousTypeError (Firefox bug 1125766).
• The User Timing API, addingPerformance.mark(),Performance.clearMarks(),Performance.measure(), andPerformance.clearMeasures() has been implemented (Firefox bug 782751).
• The prefixed version ofWindow.indexedDB,mozIndexedDB, has been removed (Firefox bug 975699).
• TheDOMContentLoaded event is no longer cancelable (Firefox bug 1134559).
• You can now useWebSockets inWorkers (Firefox bug 504553).
• TheXMLHttpRequest.responseType andXMLHttpRequest.withCredentials properties can now be set before callingXMLHttpRequest.open() (Firefox bug 707484).

MathML

No change.

SVG

No change.

Audio/Video

No change.

Networking

No change.

Security

• In Firefox, theautocomplete=false attribute is now ignored when dealing with a login form (Firefox bug 1025703). This is intended to encourage the use of more secure passwords by allowing password manager tools to work more reliably.
• RC4 is now disabled when using TLS, except for a few specifically allowed websites. This whitelist is an interim measure until those sites are fixed (Firefox bug 1124039). This fallback is controlled by thesecurity.tls.unrestricted_rc4_fallback preference,true by default for the moment (Firefox bug 1138882).
• Websites needing to fall back to an insecure version of TLS in order to work are now in a hardcoded whitelist which will shrink over time (Firefox bug 1114816). The whitelist can be disabled by settingsecurity.tls.insecure_fallback_hosts.use_static_list tofalse.

Changes for add-on and Mozilla developers

Add-on SDK

Highlights

• sdk/context-menu@2 was implemented (Firefox bug 1070952).
• sdk/addon/bootstrap was implemented (Firefox bug 1075541).
• sdk/windows/loader was removed (Firefox bug 970135).
• Fix for default language detection on Linux (Firefox bug 1114712).
• toolkit/loader now has opt-in module compatibility checking, which is enabled for all jpm add-ons (Firefox bug 1037235).

Electrolysis (E10s) updates

• sdk/page-worker e10s updates (Firefox bug 1116004).
• sdk/content/worker e10s updates (Firefox bug 1116544).
• sdk/tabs e10s updates (Firefox bug 1033838).

Details

• GitHub commits made between Firefox 37 and Firefox 38.

XUL

No change.

JavaScript code modules

Downloads.jsm

• DownloadTarget objects now haveexists andsize properties, allowing you to determine the existence of and the size of the download's target file on disk, as well as a newrefresh() method, which asks that these values be updated.

XPCOM

• "@mozilla.org/network/atomic-file-output-stream;1" and"@mozilla.org/network/safe-file-output-stream;1" now throw an exception ifPR_APPEND is passed withoutPR_TRUNCATE (Firefox bug 1117580).
• nsICompositionStringSynthesizer andnsIDOMWindowUtils.sendCompositionEvent() have been removed. Instead, usensITextInputProcessor. (Firefox bug 917322)
• nsIDOMWindowUtils.sendKeyEvent() is now deprecated. Instead, usensITextInputProcessor (Firefox bug 1119609).