Firefox 55 for developers

• Added filtering of network requests by column values and other properties (Firefox bug 1041895, Firefox bug 1354508, Firefox bug 1354507) and by using regular expressions (Firefox bug 1354495).
• Made it possible to show and hide columns within the Network Monitor (Firefox bug 862855).
• Added remote IP (Firefox bug 1344523), protocol (Firefox bug 1345489), scheme (Firefox bug 1356867), cookies and set cookies columns (Firefox bug 1356869) to Network Monitor.
• The SourceMap HTTP header is now supported (prior versions supported the deprecated X-SourceMap header, see Firefox bug 1346936).

• Elements on which contenteditable has been set to true now use <div> elements to separate different lines of text, to give Firefox parity with other modern browsers (Firefox bug 1297414). See Differences in markup generation for more details.
• Enable dom.forms.datetime by default on Nightly (Firefox bug 1366188).

• Exposed the transform-box property by default (Firefox bug 1208550).
• Implemented the frames() timing function (Firefox bug 1248340).
• Implemented the text-justify property (Firefox bug 1343512, Firefox bug 276079).
• [css-grid] fit-content unexpectedly reserves space for full clamp size in repeat() (Firefox bug 1359060).
• The float / clear logical values — inline-start and inline-end — which were previously implemented but preffed off in release channels, are now available in all channels by default (Firefox bug 1253919).
• The layout.css.variables.enabled preference has been removed completely meaning that the CSS variables feature is enabled all the time and can no longer be disabled (Firefox bug 1312328).
• Implemented the proprietary -moz-context-properties property (Firefox bug 1058040).
• Zero (0) angle value without degree unit is not correctly interpreted in linear-gradient() (Firefox bug 1363292).
• The ::cue pseudo-element is now supported; it matches on text cues presented within a media element (Firefox bug 1318542).

• The <radialGradient> fr attribute has been implemented (Firefox bug 1240275).

• The SharedArrayBuffer and Atomics objects are now enabled by default. See A Taste of JavaScript's New Parallel Primitives for an introduction to JavaScript Shared Memory and Atomics.
• The rest operator (...) is now supported in object destructuring and the spread operator (...) now works in object literals (Stage 3 ECMAScript proposal: Object Rest/Spread Properties, Firefox bug 1339395).
• Async generator methods are now supported (Firefox bug 1353693).
• The String.prototype.toLocaleLowerCase() and String.prototype.toLocaleUpperCase() methods now support an optional locale parameter to specify a language tag for locale-specific case mappings (Firefox bug 1318403).
• The Intl.Collator object now supports the caseFirst option (Firefox bug 866473).
• The Intl API now uses the browser's default locale instead of the operating system's default locale when no locale setting is provided (Firefox bug 1346674).
• Template call sites objects are now canonicalized per realm, based upon their list of raw strings (Firefox bug 1108941).
• TypedArray constructors (like Int8Array, Float32Array, etc.) have been updated to ES2017. They now use the ToIndex operation and allow constructors without arguments, which return zero-length typed arrays (Firefox bug 1317383).

New APIs

• The Collaborative Scheduling of Background Tasks API (also known as the Background Tasks API or the requestIdleCallback API) is now enabled by default after being available behind a preference since Firefox 53. This API lets you schedule tasks to be executed when the browser determines that there's free time available before the next repaint occurs, so that your code can make use of that time without causing visible performance lag (Firefox bug 1314959).
• The WebVR 1.1 API is now turned on by default on Windows (and is available on macOS in Nightly). This API exposes virtual reality devices — for example head-mounted displays like the Oculus Rift or HTC Vive — to web apps, enabling developers to translate position and movement information from the display into movement around a 3D scene, and present content into such displays.
• The Intersection Observer API — which provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport — has been added (Firefox bug 1321865).

DOM

• The Window properties scrollX and scrollY (as well as their aliases pageXOffset and pageYOffset have been updated to be subpixel precise. Instead of returning an integer, these now return a floating-point value which more accurately describes the scroll position on subpixel-precise displays (Firefox bug 1151421). If need be, you can use Math.round() to convert them into integers.
• MediaQueryList (and other related features) have been updated to match the latest spec. See Firefox bug 1354441, and also see MediaQueryList and MediaQueryListEvent.
• Methods of the DOMTokenList that modify the list value now automatically trim whitespace and remove duplicate tokens (Firefox bug 869788, also see Trimming of whitespace and removal of duplicates).
• The HTMLInputElement's maxLength property can now be dynamically altered with JavaScript after the equivalent HTML has been created (Firefox bug 1352799).
• The URL() constructor can no longer accept a DOMString as its base (2nd parameter) — it only accepts a USVString. It can still use an existing URL object for the base, which stringifies itself to the object's href attribute (Firefox bug 1368950).

DOM events

• The event types supported by the Document.createEvent() method have been updated as per the latest DOM spec (Firefox bug 1251198).
• The MessageEvent.origin property value is now of type USVString, not DOMString, and the MessageEvent.source property now takes a MessageEventSource value (which can be a WindowProxy, MessagePort, or ServiceWorker object) (Firefox bug 1311324).
• The pinch-to-zoom gesture has now been mapped to the wheel event plus the + Ctrl key. This mapping was implemented to allow developers to implement simple zooming functionality using the pinch-to-zoom gesture on mobile screens/trackpads (mousewheel + Ctrl commonly zooms) (Firefox bug 1052253).

Selection API

• The Selection API has been updated so that it has parity with other browsers in terms of how editing hosts are given focus when the selection moves inside them (Firefox bug 1318312). See Behavior of Selection API in terms of editing host focus changes for more details.
• The Selection API has been updated to match some recent spec changes (Firefox bug 1359371):
  • The collapse() and extend() methods' offset parameter is now optional.
  • The collapse() method's node parameter is now nullable.
  • The containsNode() method's partialContainment parameter is now optional.
  • The deleteFromDocument() method has been added.
• Also in the Selection API, Selection.empty() and Selection.setPosition() have been added as aliases of Selection.removeAllRanges() and Selection.collapse(), for web compat and WebKit/Blink parity reasons (Firefox bug 1359387).
• The StorageManager.persist() and StorageManager.persisted() methods of the Storage API have been implemented and exposed to Window contexts (Firefox bug 1286717).

Workers

• Workers and shared workers can now be created with an identifying name property. See the Worker() and SharedWorker() constructors, and the DedicatedWorkerGlobalScope and SharedWorkerGlobalScope interfaces. (Firefox bug 1364297).
• setTimeout() and setInterval() are now subject to minimum interval throttling for tracking scripts in background tabs — see Throttling of tracking timeout scripts (Firefox bug 1355311).

Service Workers/Push

• Messages sent to service worker contexts (e.g. as the event object of onmessage are now represented by MessageEvent objects, for consistency with other web messaging features.
• The PushManager.subscribe() method now accepts ArrayBuffers and Base64-encoded strings as applicationServerKey values (Firefox bug 1337348).

Web Audio API

• A non-standard constructor (which accepted a string enum value indicating the purpose for which the context would be used) for AudioContext interface was causing errors to be thrown when the options parameter was provided. We have removed the non-standard constructor. However, please note that the options parameter is not yet supported in Firefox and is currently ignored (Firefox bug 1361475).

WebRTC

• getUserMedia() now provides a stereo audio stream by default if the source device provides stereo sound; support to specifically request mono input will come in Firefox 56. This only works on desktop at this time; mobile Firefox does not currently support stereo audio input sources (Firefox bug 971528).
• The getUserMedia() media capabilities, constraints, and settings autoGainControl and noiseSuppression now match the spec; formerly they were moz-prefixed (Firefox bug 1366415).
• When called with an empty constraints set, getUserMedia() was incorrectly returning NotSupportedError instead of TypeError. This has been fixed (Firefox bug 1349480).
• The following new WebRTC statistics are available: framesEncoded, pliCount, nackCount, and firCount (Firefox bug 1348657).
• The RTCInboundRTPStreamStats dictionary field formerly called mozRtt has been renamed to roundTripTime to match the specification; in addition, its behavior has been adjusted to match the standard: it contains a double-precision floating point value which estimates the round-trip time based on the RTCP timestamps in the RTCP Receiver Report, measured in seconds (following the algorithm described in RFC 3550, section 6.4.1). (Firefox bug 1344970). However, please be aware that this property is moving to a different dictionary (RTCRemoteInboundRTPStreamStats) soon (Firefox bug 1380555).
• The RTCRTPStreamStats dictionary now includes the fields firCount, pliCount, and nackCount. These return low-level information that can be used to determine how reliable the connection is (Firefox bug 1348657).
• The RTCOutboundRTPStreamStats dictionary now includes the field framesEncoded, which reports the number of frames that have been successfully encoded for the stream; with this information, you can compute the frame rate (Firefox bug 1348657).
• On Android, there's now a pref to turn on hardware video encoding to improve video call performance and save on battery. To be enabled by default in Firefox 56 (Firefox bug 1265755).

Encrypted Media Extensions API

• Firefox currently allows Encrypted Media Extensions to be used in insecure contexts, despite this not being allowed in the specification. This will be changed in the near future, and starting in Firefox 55, deprecation warnings are output to the web console when this is done. (Firefox bug 1361000).
• Firefox currently doesn't require that at least one MediaKeySystemCapabilities object be included in the suggestedConfigurations parameter passed into Navigator.requestMediaKeySystemAccess(), which the specification does mandate. Starting in Firefox 55, a warning is output to the web console when any audio or video configuration is specified without specifying supported codecs. Soon, failure to include a valid configuration for one or more of audio and video will throw an exception Firefox bug 1368683).

WebGL

• The WEBGL_compressed_texture_s3tc_srgb extension is now available to WebGL and WebGL2 contexts (Firefox bug 1325113).

• The Geolocation API is now available only to secure contexts (Firefox bug 1072859).
• The Storage API is now available only to secure contexts (Firefox bug 1268804).
• The loading of mixed content is now allowed on localhost (Firefox bug 903966).
• Loading of remote JAR files has been disabled again (Firefox bug 1329336).

• Flash content is now "click-to-activate" (Firefox bug 1317856). This was immediately put into effect for all users of Nightly, and 50% of beta users. For Firefox 55 release version, the plan is to activate this for 5% of users 2 weeks after release, 25% of users 4 weeks after release, and 100% of users 6 weeks after release (Firefox bug 1365714).
• Flash and other plugins can no longer be loaded from any URL scheme except for http:// and https:// (Firefox bug 1335475).

• Firefox on Linux can now be made to run in headless mode using the -headless flag (see Firefox bug 1356681).

• The xml:base attribute can no longer be used to set the base URL for paths appearing in the style attribute, for example — <div xml:base="https://example.com/" style="background:url(picture.jpg)"></div> (Firefox bug 1350521).
• The <style> element's scoped attribute has been hidden behind a pref (layout.css.scoped-style.enabled) in content documents in Firefox 55+, as no other browsers support it.
• Support for the obscure MSThemeCompatible value of the <meta> element's http-equiv attribute has been removed from Gecko. No other modern browsers support it, and it was causing compatibility problems (Firefox bug 966240).

• The proprietary :-moz-bound-element pseudo-class has been removed (Firefox bug 1350147).
• The proprietary -moz-anchor-decoration value of text-decoration-line has been removed (Firefox bug 1355734).

• The UIEvent.isChar property has never been supported by any browser but Firefox, and it has never been fully implemented except on macOS. For that reason, it was removed in Firefox 55 to align with other browsers.
• The proprietary Firefox OS Device Storage API has been removed from the platform (Firefox bug 1299500).
• The aShowDialog parameter of the non-standard Window.find() method (which could be specified to open up a "Find" dialog in the browser) has been removed (Firefox bug 1348409).
• The HTMLFormElement.requestAutoComplete() method has been removed (see HTMLFormElement) (Firefox bug 1270740).
• The non-standard, Mozilla-specific, WebRTC offer options mozDontOfferDataChannel and mozBundleOnly have been removed from the RTCOfferOptions dictionary and are no longer supported by RTCPeerConnection.createOffer() (Firefox bug 1196974).
• Support for the proprietary Firefox OS Audio Channels API has been removed from HTMLMediaElement and AudioContext (Firefox bug 1358061).

• The SVGZoomEvent and SVGZoomEvents interfaces have been removed from the SVG2 spec and Gecko, along with the onzoom <svg> attribute (Firefox bug 1314388).

• contextMenus.create()'s command property enables you to open browser action popups, page action popups, and sidebars from the context menu.
• proxy API
• chrome_settings_overrides key enables you to override the browser's homepage.
• browser_style property enables you to have browser-like styling for browser action popups, sidebars, and options pages.
• permissions API