Firefox 41 for developers
=========================

To test the latest developer features of Firefox, install Firefox Developer Edition Firefox 41 was released on September 22, 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:

* 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[@@species]` and `Set[@@species]` getters have been added (Firefox bug 1131043).
* Non-standard let expression 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.
Older versions
--------------

* 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
* Firefox 25 for developers
* Firefox 24 for developers
* Firefox 23 for developers
* Firefox 22 for developers
* Firefox 21 for developers
* Firefox 20 for developers
* Firefox 19 for developers
* Firefox 18 for developers
* Firefox 17 for developers
* Firefox 16 for developers
* Firefox 15 for developers
* Firefox 14 for developers
* Firefox 13 for developers
* Firefox 12 for developers
* Firefox 11 for developers
* Firefox 10 for developers