Firefox 49 for developers
=========================

To test the latest developer features of Firefox, install Firefox Developer Edition Firefox 49 was released on September 20, 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
--------------------------

### Developer Tools

* JavaScript errors logged into the console now provide a [Learn more] link for additional debugging help (Firefox bug 1179876).
* CSS autocomplete: show more suggestions in autocomplete popup (Firefox bug 1260419).
* The Animation Inspector now exposes animation performance information in DevTools (Firefox bug 1254408).
* The Inspector's context menu has been reorganized to be cleaner and easier to use (Firefox bug 1211613).
* The Inspector now supports `#RRGGBBAA` and `#RGBA` syntax for color values (Firefox bug 1271191).
* The developer tools no longer display self-closing tags (such as `<br>` and `<img>` as if they have a closing tag on HTML pages; the behavior is unchanged for XHTML pages (Firefox bug 820926).
* Accessibility improvements!
    + The toolbox does a better job of ensuring that keyboard focus is more visible (Firefox bug 1242851).
    + Accessibility labels have been added to unlabeled controls (Firefox bug 1242715).
    + Added proper tree view semantics and keyboard navigation to the Inspector's markup view (Firefox bug 1242694).
* The Network Monitor now shows a Cause column, which provides an indication of what caused each particular network request (Firefox bug 1134073).
* In the *about:debugging* Add-ons page, the Reload button is only enabled for temporary add-ons. It will be disabled for all other add-ons (Firefox bug 1273184).
* In the *about:debugging* Workers page, a warning message will be displayed in the Service Workers section if service workers are incompatible with the current browser configuration (Firefox bug 1266415).
* *about:debugging* now has a new Tabs page available, which provides a complete list of all the debuggable tabs open in the current Firefox instance (Firefox bug 1266128).
* The *Disable Cache* option in the Toolbox Advanced settings has been renamed to Disable HTTP Cache, to make it clearer that this affects the HTTP cache, and not Service Workers/the Cache API (bug(1253018)).
* The Storage Inspector now allows IndexedDB databases to be deleted via their own context menus (Firefox bug 1205123), and will display warning messages if the IndexedDB cannot be deleted for some reason (if there are still active connections, for example) (Firefox bug 1268460).
### HTML

* Added support for the `<details>` and `<summary>` elements (Firefox bug 1226455).
* The `pattern` attribute of the `<input>` element now uses the `'u'` parameter in the underlying JavaScript `RegExp` (Firefox bug 1227906).
* To match a spec change, an invalid value of the `kind` attribute of the `<track>` element is now treated like `"metadata"` instead of `"subtitles"` (Firefox bug 1269712).
* The `<iframe>` element's `sandbox` attribute now supports the `'allow-popups-to-escape-sandbox'` and `'allow-modals'` values (Firefox bug 1190641).
* Support for microdata attributes and the Microdata API have been removed (Firefox bug 909633).
* The `referrerpolicy` attribute on the `<a>` element now supports the `'no-referrer-when-downgrade`' and `'origin-when-cross-origin'` (Firefox bug 1178337).
* The `form` content attribute of the `<label>` element has been removed. The `HTMLLabelElement.form` property still exists, but now returns the form with which the label's control is associated, if there is a control (and if that control is associated with a form) (Firefox bug 1268852).
### CSS

* Added `background-position-x` and `background-position-y`, which allow separately specifying the horizontal and vertical offsets at which to draw a background image; these are components of `background-position` (Firefox bug 550426).
* Added support for the `round` and `space` keywords to `background-repeat` (Firefox bug 548372).
* On `background-clip`, the keyword `text` is now activated by default (Firefox bug 1264905).
* Added support for specifying colors with an alpha channel using 4- and 8-digit CSS hex color values (#RRGGBBAA and #RGBA) (Firefox bug 567283).
* The pseudo-class `:dir` has been unprefixed (Firefox bug 859301).
* In our experimental implementation (not yet activated by default) of `clip-path`, we can now interpolate between `<basic-shape>` values (Firefox bug 1110460).
* Added the `q` length unit (Firefox bug 1274526).
* The property `text-align-last` has been unprefixed (Firefox bug 1039541).
* Added support for `overflow-wrap`, replacing `word-wrap` that is still supported as an alternative name (Firefox bug 955857).
* Our experimental CSS Grids implementation has been improved:
    + Implemented `<percentage>` for the `grid-gap`, `grid-row-gap`, and `grid-column-gap` properties (Firefox bug 1266268).
    + Implemented grid layout support for `align`, `justify-self``:baseline` and `last-baseline` (aka "baseline self-alignment") (Firefox bug 1221525).
    + Implemented grid item baseline content alignment (Firefox bug 1256429).
* Our experimental CSS Masks implementation has been improved:
    + The `mask-origin` property now uses `border-box` instead of `padding-box` as initial value, to match the spec (Firefox bug 1258286).
    + The `mask-repeat` property now supports the `space` and `round` values (Firefox bug 1258626).
    + Fixed an issue preventing the `mask-position` attribute from being animated (Firefox bug 1273804).
* The preference controlling `text-emphasis` has been removed, so support for this property can no longer be disabled (Firefox bug 1229609).
### JavaScript

* The ES2015 `getPrototypeOf()` and `setPrototypeOf()` `Proxy` traps have been implemented (Firefox bug 888969).
* The ES2015 `RegExp.prototype[@@match]()`, `RegExp.prototype[@@replace]()`, `RegExp.prototype[@@search]()`, and `RegExp.prototype[@@split]()` methods, and `RegExp[@@species]` getter have been implemented (Firefox bug 887016).
* The deprecated, non-standard `flags` argument of `String.prototype.``match`/`search`/`replace` has been removed (Firefox bug 1108382).
* The behavior of the `Date.parse()` method when parsing 2-digit years has been changed to be more interoperable with the Google Chrome browser (Firefox bug 1265136).
### Interfaces/APIs/DOM

#### DOM & HTML DOM

* The method `DOMTokenList.supports()` has been added (Firefox bug 1257849).
* The `DOMTokenList.replace()` method has been added (Firefox bug 1224186).
* Leading `'?'` characters are now ignored in the parameter of the `URLSearchParams()` constructor (Firefox bug 1268361).
* The value returned by `URL.origin`, `HTMLAnchorElement.origin`, and `HTMLAreaElement.origin` for URL using the `blob:` scheme is no longer incorrectly `null` but is instead the origin of the URL formed by removing the leading `blob:` (Firefox bug 1270451).
* In prerendering mode, the `Document.visibilityState` property now returns `'prerender'` (Firefox bug 1069772).
* The `isSecureContext` property has been implemented (Firefox bug 1162772).
* The DOM4 `Element.before`, `Element.after`, `Element.replaceWith`, `Element.append` and `Element.prepend` methods have been implemented (Firefox bug 911477).
* The `TouchList.identifiedTouch()` method has been removed (Firefox bug 1188539).
* By default, the `scrollbars` `Window` feature is enabled when calling `Window.open()`. In the past, while it was strongly recommended to enable it, it wasn't the default (Firefox bug 1257887).
* Added the *experimental* and *non-standard* `HTMLMediaElement.seekToNextFrame()` method, which allows seeking frame-by-frame through video content (Firefox bug 1235301). While you're encouraged to experiment with this method to help us understand how useful it is, *do not use it in production code!*
* The `HTMLLabelElement.form` property now returns the form with which the label's control is associated, if there is a control (and if that control is associated with a form). Previously, labels were directly associated with forms using this property (Firefox bug 1268852).
* Support for the third parameter of `EventTarget.addEventListener()`, either a `Boolean` or an `EventListenerOptions` has been added (Firefox bug 1266164 and Firefox bug 1266066).
* The audio volume related values for `KeyboardEvent.key` have been renamed. `"VolumeDown"` is now `"AudioVolumeDown"`, `"VolumeUp"` is now `"AudioVolumeUp"`, and `"VolumeMute"` is now `"AudioVolumeMute".` This brings Firefox into alignment with the latest draft of the UI Events specification (Firefox bug 1272578). See Code values for keyboard events for a full list of available key codes.
* The keys previously referred to as `"MozHomeScreen"`, `"MozCameraFocusAdjust"`, and `"MozPhoneCall"` now have official names in the UI Events specification: `"GoHome"`, `"CameraFocus"`, and `"Call"`. Firefox 49 has been updated to use the new names (Firefox bug 1272599). See Code values for keyboard events for a full list of available key codes.
* The key values `"Separator"` and `"MediaSkip"` have been removed, as they were deprecated and unused (Firefox bug 1232919).
* Key values and the corresponding key codes `"Hyper"` and `"Super"` have been added to represent these legacy modifier keys (Firefox bug 1232919).
* Two key values for multimedia numeric keypad keys have been added: `"Key11"` and `"Key12"` (Firefox bug 1232919).
* The following new key values have been added for audio control keys: `"AudioBassBoostToggle"`, `"AudioTrebleDown"`, and `"AudioTrebleUp"` (Firefox bug 123919).
* Key values have been added for these microphone control keys: `MicrophoneToggle`, `MicrophoneVolumeDown`, `MicrophoneVolumeUp`, and `MicrophoneVolumeMute` (Firefox bug 123919).
* New key values have been added to support speech recognition devices: `SpeechCorrectionList` and `SpeechInputToggle` (Firefox bug 1232919).
* New key values have been added to support special buttons on phones: `AppSwitch`, `Call`, `CameraFocus`, `EndCall`, `GoBack`, `GoHome`, `HeadsetHook`, `LastNumberRedial`, `Notification`, `MannerMode`, and `VoiceDial` (Firefox bug 1232919).
* These new application key values have been added: `LaunchContacts` and `LaunchPhone` (Firefox bug 1232919).
* New key values have been added to support television devices: `TV3DMode`, `TVAntennaCable`, `TVAudioDescription`, `TVAudioDescriptionMixDown`, `TVAudioDescriptionMixUp`, `TVContentsMenu`, `TVDataService`, `TVInput`, `TVInputComponent1`, `TVInputComponent2`, `TVInputComposite1`, `TVInputComposite2`, `TVInputHDMI1`, `TVInputHDMI2`, `TVInputHDMI3`, `TVInputHDMI4`, `TVInputVGA1`, `TVMediaContext`, `TVNetwork`, `TVNumberEntry`, `TVRadioService`, `TVSatellite`, `TVSatelliteBS`, `TVSatelliteCS`, `TVSatelliteToggle`, `TVTerrestrialAnalog`, `TVTerrestrialDigital`, `TVTimer`, and `DVR` (Firefox bug 1232919).
* The key value `MediaSelect` has been replaced with the standard `LaunchMediaPlayer` key value (Firefox bug 1272592).
* Additional media player key values have been added as well. These are `MediaAudioTrack`, `MediaSkipBackward`, `MediaSkipForward`, `MediaStepBackward`, `MediaStepForward`, `MediaTopMenu`, `NavigateIn`, `NavigateNext`, `NavigateOut`, and `NavigatePrevious` (Firefox bug 1232919).

#### Canvas

* The `CanvasRenderingContext2D.filter` property, which provides support for adding filters to a canvas, is now activated by default and no longer needs to be enabled using a preference (Firefox bug 1173545).

#### WebGL

* The `EXT_color_buffer_float` WebGL 2 extension has been implemented (Firefox bug 1129332).
* The `webglcontextcreationerror` event, which is sent when a WebGL context creation attempt fails, has been implemented (Firefox bug 1271478). Use this to help understand what went wrong, both for debugging and for production error handling.

#### IndexedDB

* You can now rename IndexedDB indexes; the `IDBIndex.name` property is no longer read-only (Firefox bug 1118028).
* You can also now rename `IDBObjectStore`s; the `IDBObjectStore.name` property is no longer read-only (Firefox bug 1118028).

#### Service Workers and related

* The Fetch API's `Response` object now implements the `redirected` property, which indicates whether or not the response is for a request which was redirected. Please review the security related notes in the documentation before using this property (Firefox bug 1243792).
* In the Permissions API, Firefox no longer supports the 'push' `PermissionDescriptor` dictionary type (referred to in the spec as `PushPermissionDescriptor`); this is because Firefox relies on a quota system for controlling the `userVisibleOnly` status instead, and was throwing an error when it encountered a `PushPermissionDescriptor` instance (Firefox bug 1266821). With this dictionary removed, Firefox now ignores it.

#### Media Streams

* In the past, it was possible for a call to `MediaDevices.getUserMedia()` which requests both audio and video to succeed in cases where the user has only one of the two types of hardware available. This has been fixed (Firefox bug 802326).
* In prior versions of Firefox, it was possible for a call to `MediaDevices.getUserMedia()` which requests both audio and video to succeed even though the user denied access to one but not both of the matching devices. This has been fixed (Firefox bug 802326). This involves minor user interface changes as well, to remove the options to choose "No audio" or "No video" when the user is prompted for permissions.
* The `MediaStream.getTrackById()` method has been implemented (Firefox bug 1208390).

#### WebRTC

* The `RTCPeerConnection.addTrack()` method has been updated to allow tracks which are not components of the specified streams to be added to the connection. Instead, the streams are used to group tracks on the receiving end of the connection (Firefox bug 1271669).

#### New APIs

* The `PerformanceObserver` API is now activated by default on Nightly. It is not available by default in other versions of Firefox 49 (Firefox bug 1271487).

#### Others

* `XMLHttpRequest.getResponseHeader()` and `XMLHttpRequest.getAllResponseHeaders()` return empty headers in case the preference `network.http.keep_empty_response_headers_as_empty_string` is set to `true` (Firefox bug 669259).
* The Firefox OS-only Data Store API has been removed (Firefox bug 1261009).
* The Fullscreen API event handlers `Document.onfullscreenchange` and `Document.onfullscreenerror` have been removed from `Element` as they were never fired there; the prefixed versions of these event handlers have been kept there for compatibility purposes, however (Firefox bug 1270386). Note that this is not yet activated by default, but is behind the `full-screen-api.unprefix.enabled` preference (Firefox bug 1268749).
* The obsolete `Document.mozFullScreen` property has been unprefixed to `Document.fullscreen` Firefox bug 1269157. Note that this is not yet activated by default by behind the `full-screen-api.unprefix.enabled` preference (Firefox bug 1268749).
* The read-only properties `Document.fullscreenElement` and `Document.fullscreenEnabled` no longer throw an exception if an attempt is made to change their values; instead, the new value is silently ignored and the setter function is a no-op (Firefox bug 1269798).
* Any kind of data can now be retrieved from the clipboard using `DataTransfer.getData()`: previously, only data of certain MIME types were supported Firefox bug 860857.
* Our implementation of the Frame Timing API, consisting of the two interfaces `PerformanceCompositeTiming` and `PerformanceRenderTiming`, has been removed as the spec has been completely rewritten (Firefox bug 1271846).
* To match the spec, the `VTTCue.positionAlign` property now returns a `PositionAlign` enum instead of an `Align` enum (Firefox bug 1276129).
* The speech synthesis part of Web Speech API is now activated by default (Firefox bug 1268633).
* The Performance Timeline API is now available by default in Nightly (though not in Aurora, Beta or Release).
* The `install` event, and the `Window.oninstall` event handler, are now supported for Web Manifests (Firefox bug 1265279).
* When using the `AudioContext.createPeriodicWave()` method of the Web Audio API, you can now specify whether the resulting periodic wave should be normalized by including a dictionary object as the third parameter, which includes a single parameter — `{disableNormalization: true}` (Firefox bug 1265405).
* In the WebVTT API, `VTTCue.positionAlign` now correctly returns a `PositionAlignSetting` enum as per spec; previously it returned an `AlignSetting` enum (Firefox bug 1276129).
* The Speech Synthesis part of the Web Speech API is now enabled by default across all desktop browsers (Firefox bug 1268633).
* The `Animation()` constructor of the Web Animations API now accepts a null timeline (Firefox bug 1096776).
* The `KeyframeEffect` property `target` is now supported in Firefox, if you have enabled Web Animations (Firefox bug 1067769).
### MathML

*No change.*

### SVG

* Removed support for the deprecated `<altGlyph>`, `<altGlyphDef>` and `<altGlyphItem>` elements (Firefox bug 1260032).
### Audio/Video

*No change.*

### Plugins and Flash

Beginning in Firefox 49, Firefox, by default, blocks certain kinds of Flash content that aren't necessary for sites to function well. This behavior, controlled by the preference `browser.safebrowsing.blockedURIs.enabled`, helps to improve the performance of sites and Firefox in general without having significant impact on site usability. It also helps improve stability of the browsing experience by eliminating a major cause of crashes. The blocked Flash modules include several used just for fingerprinting purposes, as well as a number of "supercookie" modules, and in the future may be expanded to include more types of blocked modules. See Firefox bug 1275591 for details.

This marks the next step in the journey toward a plugin-free future. HTML is very close to the point where plugins will no longer be needed to get the job done.

HTTP
----

* The `Cache-Control: immutable` directive has been implemented (Firefox bug 1267474). See also this blog post for more information.
* The `require-sri-for` `Content-Security-Policy` has been implemented (Firefox bug 1265318).
Networking
----------

* The Proxy Auto-Configuration (PAC) implementation has been updated. Now `weekdayRange`, `dateRange`, and `timeRange` support "reversed ranges", for example, `weekdayRange("SAT", "MON")` will evaluate `true` if the current day is Saturday, Sunday, or Monday (Firefox bug 1251332).
Security
--------

* The `isSecureContext` property, indicating whether a context is capable of using features that require secure contexts, has been implemented (Firefox bug 1162772).
Compatibility
-------------

In order to improve compatibility with existing content, Firefox now accepts some WebKit prefixed properties and attributes.

* The following properties now also work prefixed with `-webkit`:
    + `-webkit-align-items`
    + `-webkit-align-content`
    + `-webkit-align-self`
    + `-webkit-animation`
    + `-webkit-animation-delay`
    + `-webkit-animation-direction`
    + `-webkit-animation-duration`
    + `-webkit-animation-fill-mode`
    + `-webkit-animation-iteration-count`
    + `-webkit-animation-name`
    + `-webkit-animation-play-state`
    + `-webkit-animation-timing-function`
    + `-webkit-backface-visibility`
    + `-webkit-background-clip`
    + `-webkit-background-origin`
    + `-webkit-background-size`
    + `-webkit-border-bottom-left-radius`
    + `-webkit-border-bottom-right-radius`
    + `-webkit-border-image`
    + `-webkit-border-top-left-radius`
    + `-webkit-border-top-right-radius`
    + `-webkit-border-radius`
    + `-webkit-box-shadow`
    + `-webkit-filter`
    + `-webkit-flex`
    + `-webkit-flex-basis`
    + `-webkit-flex-direction`
    + `-webkit-flex-flow`
    + `-webkit-flex-grow`
    + `-webkit-flex-shrink`
    + `-webkit-flex-wrap`
    + `-webkit-justify-content`
    + `-webkit-order`
    + `-webkit-perspective`
    + `-webkit-perspective-origin`
    + `-webkit-text-size-adjust`
    + `-webkit-transform`
    + `-webkit-transform-origin`
    + `-webkit-transform-style`
    + `-webkit-transition`
    + `-webkit-transition-delay`
    + `-webkit-transition-duration`
    + `-webkit-transition-property`
    + `-webkit-transition-timing-function`
    + `-webkit-user-select`
* The following properties map to the equivalent prefixed property:
    + `-webkit-box-flex`
    + `-webkit-box-ordinal-group`
    + `-webkit-box-orient`
    + `-webkit-box-align`
    + `-webkit-box-pack`
* For `<image>` values:
    + The following functions map to their unprefixed equivalents: `-webkit-linear-gradient()`, `-webkit-radial-gradient()`, `-webkit-repeating-linear-gradient()`, and `-webkit-repeating-radial-gradient()`.
    + The outdated `-webkit-gradient` is supported (and translated to a regular gradient)
* The following `display` values are translated:
    + `-webkit-box` to `-moz-box`
    + `-webkit-flex` to `flex`
    + `-webkit-inline-box` to `inline-flex`
    + `-webkit-inline-flex` to `-moz-inline-flex`
* The following properties are supported (and don't map to any unprefixed equivalent):
    + `-webkit-text-fill-color`
    + `-webkit-text-stroke-color`
    + `-webkit-text-stroke-width`
    + `-webkit-text-stroke`
* The `WebKitCSSMatrix` interface is an alias of `DOMMatrix`
* The following media query features have been implemented:
    + `-webkit-min-device-pixel-ratio` as an alias of `min-resolution` with the same value (in `dppx)`, though this feature is disabled by default (behind about:config pref `layout.css.prefixes.device-pixel-ratio-webkit`)
    + `-webkit-max-device-pixel-ratio` as an alias of `max-resolution` of the same value (in `dppx`); this feature is also disabled by default, behind the same about:config pref.
    + `-webkit-transform-3d` always matching, indicating 3d transform support.
Changes for add-on and Mozilla developers
-----------------------------------------

### WebExtensions

* Support for the `history` has been added. This provides access to the browser history, with methods available for searching the history, getting information about previously-visited pages, and adding and removing history entries.
* Added the `tabs.removeCSS()` method to the tabs API. This method lets you remove CSS which was previously injected by calling `tabs.insertCSS()`.
### Interfaces

* In `EventTarget.addEventListener()`, the value `mozSystemGroup`, active only in code running in XBL or in Firefox's chrome, is a `Boolean` which indicates if the listener is added to the system group. (Firefox bug 1274520)
### Other

*No change.*

Older versions
--------------

* 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
* 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