Firefox 41 release notes for developers

Changes for Web developers

Developer Tools

Highlights:

• Take a screenshot of a DOM node
• Copy as HAR/save as HAR
• "Add Rule" button in the Rules view
• View source in a tab (Disabled by default)
• More options to copy CSS rules
• Copy image as data: URL in the Rules view
• Added command to GCLI to display CSP info

All devtools bugs fixed between Firefox 40 and Firefox 41: note that many of these bugs, especially those relating to the performance tools, were uplifted to Firefox 40.

CSS

• Support for laying out vertical scripts has been activated by default (Firefox bug 1138384). That means that the following CSS properties are now available:

  • Choosing the direction of writing: writing-mode.
  • Controlling orientation of characters: text-orientation.
  • Direction-independent equivalents of width and height: block-size and inline-size.
  • Direction-independent equivalents of min-width and min-height: min-block-size and min-inline-size.
  • Direction-independent equivalents of max-width and max-height: max-block-size and max-block-size.
  • Direction-independent equivalents of margin-top, margin-right, margin-bottom and margin-left: margin-block-start, margin-block-end, margin-inline-start and margin-inline-end.
  • Direction-independent equivalents of padding-top, padding-right, padding-bottom and padding-left: padding-block-start, padding-block-end, padding-inline-start and padding-inline-end.
  • Direction-independent equivalents of border-top, border-right, border-bottom and border-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 and border-inline-end-color.
  • Direction-independent equivalents of top, right, bottom and left: offset-block-start, offset-block-end, offset-inline-start and offset-inline-end.

• Support the transform-origin property in SVG and implement the transform-box property (Firefox bug 923193).

HTML

• <a> without an href attribute is no longer classified as interactive content. Clicking it inside <label> will activate labelled content (Firefox bug 1167816).
• SVG icons are now supported for site icons, that is favicons and shortcut icons (Firefox bug 366324).
• The crossorigin attribute is now supported for <link rel='preconnect'> (Firefox bug 1174152).
• The picture element does not react to resize/viewport changes (Firefox bug 1135812).

JavaScript

• Date.prototype is now an ordinary object, not a Date instance anymore (Firefox bug 861219).
• Date.prototype.toString is now a generic method (Firefox bug 861219).
• Symbol.species has been added (Firefox bug 1131043).
• Map[Symbol.species] and Set[Symbol.species] getters have been added (Firefox bug 1131043).
• Non-standard let expressions support has been dropped (Firefox bug 1023609).
• Destructured parameters with default value assignment are now supported (Firefox bug 1018628).
• Per ES2015, curly braces are required for method definitions. Syntax without them will fail from now on (Firefox bug 1150855).
• Method definitions (except for generator methods) are not constructable anymore (Firefox bug 1059908 and Firefox bug 1166950).
• As part of ES2015 specification compliance, parenthesized destructuring patterns, like ([a, b]) = [1, 2] or ({a, b}) = { a: 1, b: 2 }, are now considered invalid and will throw a SyntaxError. See Jeff Walden's blog post for more details.
• The new.target syntax has been added (Firefox bug 1141865).

Interfaces/APIs/DOM

HTML Editing API

• Cut, copy and paste commands handling has been revamped and now allow programmatic copying and cutting from JS for Web content:
  • With the 'paste' command as argument, Document.queryCommandSupported() now returns false if has insufficient privileges to actually perform the action (Firefox bug 1161721).
  • With the 'cut' or 'copy' command as argument, Document.queryCommandSupported() now returns true if called within the context of a user-initiated or privileged code (Firefox bug 1162952).
  • With the 'cut' or 'copy' command as argument, Document.execCommand() now works, but only within the context of user-initiated or privileged code (Firefox bug 1012662).
  • Instead of raising an exception, Document.execCommand() when the command is not supported or enabled (Firefox bug 1027560).

Events

• The non-standard initCloseEvent() method of the CloseEvent event and the ability to create a CloseEvent using the document.createEvent('CloseEvent') method has been removed; use the standard constructor, CloseEvent() instead (Firefox bug 1161950).
• On Desktop, PointerEvent is now activated by default in Nightly; it is not activated in Developer Edition, Beta or Release and won't be for at least some versions (Firefox bug 1166347).
• The unprefixed version of MouseEvent.movementX and MouseEvent.movementY have been added; the prefixed versions are deprecated and will be removed at some point in the future (Firefox bug 1164981).

Web Crypto

• SubtleCrypto.importKey() and SubtleCrypto.exportKey() now supports ECDH keys (Firefox bug 1050175).

Canvas API

• HTMLCanvasElement.captureStream() and CanvasCaptureMediaStream have been added and allow to stream the display of a <canvas> in real-time (Firefox bug 1032848).
• MediaStream.id now returns the unique id of a stream (Firefox bug 1089798).
• The initial value of CanvasRenderingContext2D.filter is now correctly set to none (Firefox bug 1163124).

Service Workers

• Improvement to our experimental Service Worker implementation:

  • ServiceWorkerGlobalScope.skipWaiting() has been implemented (Firefox bug 1131352).
  • Clients.claim() has been added (Firefox bug 1130684).
  • The other functional events of Service Workers have been made to inherit from ExtendableEvent, giving them access to the waitUntil() method (Firefox bug 1160527).

• The CacheStorage and Cache interfaces are now supported (Firefox bug 1110144).

WebGL

• The failIfMajorPerformanceCaveat WebGL context attribute has been added and can be set when creating a WebGL context with HTMLCanvasElement.getContext() to indicate if a context creation should fail if the system performance is low (Firefox bug 1164970).

WebRTC

• Firefox no longer offers a default STUN server to be used if none are specified when constructing a new RTCPeerConnection. You'll need to provide one in order to successfully establish a WebRTC connection.

Miscellaneous

• On OS X and Windows, Navigator.onLine now changes regarding network connectivity (it always returned true, unless "Work offline" mode was selected) before (Firefox bug 654579).
• MessagePort and MessageChannel now available in Web workers, and are enabled by default in all contexts (Firefox bug 952139) and (Firefox bug 911972).
• The User Timing API is now available in Web workers (Firefox bug 1155761).
• The Notifications API is now available in Web workers (Firefox bug 916893).
• DOMRequest and DOMCursor are now available in Web workers (Firefox bug 1167650).
• The CSS Font Loading API has been completely implemented and is now enabled by default (Firefox bug 1149381).
• Shared workers can no longer be shared between private (i.e., browsing in a private window) and non-private documents (see Firefox bug 1177621).
• The URL.searchParams property is now read-only (Firefox bug 1174731).
• The HTMLAnchorElement.hash property no longer decodes URL fragment (Firefox bug 1093611).

MathML

New default and fallback font handling

Mathematical formulas require special fonts. So far, these fonts were hard-coded in the mathml.css user agent stylesheet (which sets the font-family on <math> tag) and in the preference option font.mathfont-family (which sets the fallback fonts to use for stretchy and large operators). Firefox 41 introduces an internal x-math language that is automatically set on the <math> tag as well as corresponding preference options (e.g., font.name.serif.x-math). The user agent stylesheet now sets font-family to serif on the <math> tag and the preference option font.mathfont-family is replaced with font.name.serif.x-math. All platforms now essentially use the same list of fallback fonts, with "Latin Modern Math" as the first one. The default/fallback fonts can be configured from the standard per-language font preference menu. For more details, see Firefox bug 947654 and Firefox bug 1160456.

SVG

• Site icons (favicons, shortcut icons) now support SVG (Firefox bug 366324).

Audio/Video

• The media.autoplay.enabled preference now also applies to untrusted HTMLMediaElement.play() invocations too, that is calls from non-users activated scripts (Firefox bug 659285).

Networking

• The X-Content-Duration header is no longer supported (Firefox bug 1160695).
• Draft versions of the HTTP/2 protocol are no more supported (Firefox bug 1132357).

Security

• The CSP 1.1 manifest-src directive is now supported (Firefox bug 1089255).
• Previous versions of Firefox incorrectly expected the Content Security Policy referrer directive's value origin-when-cross-origin to be spelled origin-when-crossorigin. This has been corrected to include the missing dash character.

Changes for add-on and Mozilla developers

XUL

No change.

JavaScript code modules

No change.

XPCOM

Interfaces

No change.

Other

• A new, internal, and chrome-context-only API to render the root widget of a window into a <canvas> has been added: CanvasRenderingContext2D.drawWidgetAsOnScreen(). This API uses the operating system to snapshot the widget on-screen. For more details see Firefox bug 1167477.