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 (bug 1179876).
• CSS autocomplete: show more suggestions in autocomplete popup (bug 1260419).
• The Animation Inspector now exposes animation performance information in DevTools (bug 1254408).
• The Inspector's context menu has been reorganized to be cleaner and easier to use (bug 1211613).
• The Inspector now supports #RRGGBBAA and #RGBA syntax for color values (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 (bug 820926).
• Accessibility improvements!
  • The toolbox does a better job of ensuring that keyboard focus is more visible (bug 1242851).
  • Accessibility labels have been added to unlabeled controls (bug 1242715).
  • Added proper tree view semantics and keyboard navigation to the Inspector's markup view (bug 1242694).
• The Network Monitor now shows a Cause column, which provides an indication of what caused each particular network request (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 (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 (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 (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 (bug 1205123), and will display warning messages if the IndexedDB cannot be deleted for some reason (if there are still active connections, for example) (bug 1268460).

HTML

• Added support for the <details> and <summary> elements (bug 1226455).
• The pattern attribute of the <input> element now uses the 'u' parameter in the underlying JavaScript RegExp (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" (bug 1269712).
• The <iframe> element's sandbox attribute now supports the 'allow-popups-to-escape-sandbox' and 'allow-modals' values (bug 1190641).
• Support for microdata attributes and the Microdata API have been removed (bug 909633).
• The referrerpolicy attribute on the <a> element now supports the 'no-referrer-when-downgrade' and 'origin-when-cross-origin' (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) (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 (bug 550426).
• Added support for the round and space keywords to background-repeat (bug 548372).
• On background-clip, the keyword text is now activated by default (bug 1264905).
• Added support for specifying colors with an alpha channel using 4- and 8-digit CSS hex color values (#RRGGBBAA and #RGBA) (bug 567283).
• The pseudo-class :dir() has been unprefixed (bug 859301).
• In our experimental implementation (not yet activated by default) of clip-path, we can now interpolate between <basic-shape> values (bug 1110460).
• Added the q length unit (bug 1274526).
• The property text-align-last has been unprefixed (bug 1039541).
• Added support for overflow-wrap, replacing word-wrap that is still supported as an alternative name (bug 955857).
• Our experimental CSS Grids implementation has been improved:
  • Implemented <percentage> for the grid-gap, grid-row-gap, and grid-column-gap properties (bug 1266268).
  • Implemented grid layout support for align, justify-self:baseline and last-baseline (aka "baseline self-alignment") (bug 1221525).
  • Implemented grid item baseline content alignment (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 (bug 1258286).
  • The mask-repeat property now supports the space and round values (bug 1258626).
  • Fixed an issue preventing the mask-position attribute from being animated (bug 1273804).
• The preference controlling text-emphasis has been removed, so support for this property can no longer be disabled (bug 1229609).

JavaScript

• The ES2015 getPrototypeOf() and setPrototypeOf() Proxy traps have been implemented (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 (bug 887016).
• The deprecated, non-standard flags argument of String.prototype.match/search/replace has been removed (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 (bug 1265136).

Interfaces/APIs/DOM

DOM & HTML DOM

• The method DOMTokenList.supports() has been added (bug 1257849).
• The DOMTokenList.replace() method has been added (bug 1224186).
• Leading '?' characters are now ignored in the parameter of the URLSearchParams() constructor (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: (bug 1270451).
• In prerendering mode, the Document.visibilityState property now returns 'prerender' (bug 1069772).
• The Window.isSecureContext property has been implemented (bug 1162772).
• The DOM4 ChildNode.before(), ChildNode.after(), ChildNode.replaceWith(), ParentNode.append() and ParentNode.prepend() methods have been implemented (bug 911477).
• The TouchList.identifiedTouch() method has been removed (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 (bug 1257887).
• Added the experimental and non-standard HTMLMediaElement.seekToNextFrame() method, which allows seeking frame-by-frame through video content (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 (bug 1268852).
• Support for the third parameter of EventTarget.addEventListener(), either a Boolean or an EventListenerOptions has been added (bug 1266164 and 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 (bug 1272578). See "Code values" in KeyboardEvent.code 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 (bug 1272599). See "Code values" in KeyboardEvent.code for a full list of available key codes.
• The key values "Separator" and "MediaSkip" have been removed, as they were deprecated and unused (bug 1232919).
• Key values and the corresponding key codes "Hyper" and "Super" have been added to represent these legacy modifier keys (bug 1232919).
• Two key values for multimedia numeric keypad keys have been added: "Key11" and "Key12" (bug 1232919).
• The following new key values have been added for audio control keys: "AudioBassBoostToggle", "AudioTrebleDown", and "AudioTrebleUp" (bug 123919).
• Key values have been added for these microphone control keys: "MicrophoneToggle", "MicrophoneVolumeDown", "MicrophoneVolumeUp", and "MicrophoneVolumeMute" (bug 123919).
• New key values have been added to support speech recognition devices: "SpeechCorrectionList" and "SpeechInputToggle" (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" (bug 1232919).
• These new application key values have been added: "LaunchContacts" and "LaunchPhone" (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" (bug 1232919).
• The key value "MediaSelect" has been replaced with the standard "LaunchMediaPlayer" key value (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" (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 (bug 1173545).

WebGL

• The EXT_color_buffer_float WebGL 2 extension has been implemented (bug 1129332).
• The webglcontextcreationerror event, which is sent when a WebGL context creation attempt fails, has been implemented (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 (bug 1118028).
• You can also now rename IDBObjectStores; the IDBObjectStore.name property is no longer read-only (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 (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 (bug 1266821). With this dictionary removed, Firefox now simply 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 (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 (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 (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 (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 (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 (bug 669259).
• The Firefox OS-only Data Store API has been removed (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 (bug 1270386). Note that this is not yet activated by default, but is behind the full-screen-api.unprefix.enabled preference (bug 1268749).
• The obsolete Document.mozFullScreen property has been unprefixed to Document.fullscreen bug 1269157}. Note that this is not yet activated by default by behind the full-screen-api.unprefix.enabled preference (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 (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 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 (bug 1271846).
• To match the spec, the VTTCue.positionAlign property now returns a PositionAlign enum instead of an Align enum (bug 1276129).
• The speech synthesis part of Web Speech API is now activated by default (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 (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} (bug 1265405).
• In the WebVTT API, VTTCue.positionAlign now correctly returns a PositionAlignSetting enum as per spec; previously it returned an AlignSetting enum (bug 1276129).
• The Speech Synthesis part of the Web Speech API is now enabled by default across all desktop browsers (bug 1268633).
• The Animation() constructor of the Web Animations API now accepts a null timeline (bug 1096776).

MathML

No change.

SVG

• Removed support for the deprecated <altGlyph>, <altGlyphDef> and <altGlyphItem> elements (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 elminating 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 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 (bug 1267474). See also this blog post for more information.
• The require-sri-for Content-Security-Policy has been implemented (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 (bug 1251332).

Security

• The Window.isSecureContext property, indicating whether a context is capable of using features that require secure contexts, has been implemented (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. (bug 1274520)

Other

No change.

See also

• Site Compatibility for Firefox 49

Older versions