Firefox 58 for developers

This article provides information about the changes in Firefox 58 that will affect developers. Firefox 58 was released on January 23, 2018.

• The Shape Path Editor has been enabled by default for shapes generated via clip-path (bug 1405339).
• The Network Monitor now has a button to pause/play recording of network traffic (bug 1005755).
• In the Network Monitor the "Flash" filter button is no longer available, and Flash requests are included in the "Others" filter (bug 1413540).
• The code for the old Responsive Design Mode (enabled by default pre-Firefox 52) has now been removed from the Devtools (bug 1305777). See Responsive Design Mode for information on the new tools.
• The option to view MDN docs from the CSS pane of the page inspector has been removed (bug 1382171) (was disabled since 55, bug 1352801).

No changes.

• The font-display descriptor is now available by default on all platforms (bug 1317445).

No changes.

• The Promise.prototype.finally() method has been implemented (bug 1019116).
• The Intl.PluralRules object has been implemented (bug 1403318).
• The Intl.NumberFormat.prototype.formatToParts() method has been implemented (bug 1403319).
• The Intl.DateTimeFormat object now supports the hourCycle option and the hc language tag (bug 1386146).
• The optional catch binding proposal has been implemented (bug 1380881).

New APIs

• The PerformanceNavigationTiming API has been implemented (bug 1263722).
  • Gecko has also been given a pref that can be used to disable the interface if required — dom.enable_performance_navigation_timing, defaulting to true (bug 1403926).

DOM

• Errors reported via error objects in certain APIs — for example in the error property of FileReader, IDBRequest, and IDBTransaction, and when requests made via certain methods of RTCPeerConnection are unsuccessful — are now represented by DOMException instances. DOMError is now deprecated, having been removed from the DOM4 spec (bug 1120178).
• The PerformanceResourceTiming.workerStart property is now supported (bug 1191943).
• Budget-based background timeout throttling has been implemented — see Policies in place to aid background page performance for more details (bug 1377766).

DOM events

No changes.

Media and WebRTC

• The prefixed version of HTMLMediaElement.srcObject has been removed; make sure code is updated to use the standard srcObject instead of mozSrcObject (bug 1183495).
• Using MediaStream.addTrack() to add tracks to a stream obtained using getUserMedia(), then attempting to record the resulting stream now works as expected. Previously, only the tracks originally included in the stream returned by getUserMedia() were being included in the recorded media (bug 1296531).
• The WebVTT VTTRegion interface has always been created when interpreting WebVTT files, but the resulting regions were not previously utilized. Starting in Firefox 58, they are, if you enable the preference media.webvtt.regions.enabled by setting its value to true.

Canvas and WebGL

• Support for prefixed WebGL extensions has been removed (bug 1403413):
  • For MOZ_WEBGL_compressed_texture_atc use WEBGL_compressed_texture_atc instead.
  • For MOZ_WEBGL_compressed_texture_pvrtc use WEBGL_compressed_texture_pvrtc instead.
  • For MOZ_WEBGL_compressed_texture_s3tc use WEBGL_compressed_texture_s3tc instead.
  • For MOZ_WEBGL_depth_texture use WEBGL_depth_texture instead.
  • For MOZ_WEBGL_lose_context use WEBGL_lose_context instead.

• frame-ancestors is no longer ignored in Content-Security-Policy-Report-Only (bug 1380755).
• Firefox now implements a TLS handshake timeout with a default value of 30 seconds. The timeout value can be varied by editing the network.http.tls-handshake-timeout pref in about:config (bug 1393691).
• The worker-src CSP directive has been implemented (bug 1302667).
• The 425: Too Early status code and related Early-Data request header are now supported (bug 1406908).

No changes.

No changes.

• "Add to home screen" is now supported in Firefox for Android, part of the Progressive Web Apps effort (bug 1212648).
• WebAssembly now has a tiered compiler providing load time optimizations (bug 1277562), and new streaming APIs — WebAssembly.compileStreaming() and WebAssembly.installStreaming() bug 1347644.

• You can no longer nest an <a> element inside a <map> element to create a hotspot region — an <area> element needs to be used instead (bug 1317937).

• The following proprietary Mozilla system metric pseudo-classes are no longer available to web content (bug 1396066):
  • :-moz-system-metric(images-in-menus)
  • :-moz-system-metric(mac-graphite-theme)
  • :-moz-system-metric(scrollbar-end-backward)
  • :-moz-system-metric(scrollbar-end-forward)
  • :-moz-system-metric(scrollbar-start-backward)
  • :-moz-system-metric(scrollbar-start-forward)
  • :-moz-system-metric(scrollbar-thumb-proportional)
  • :-moz-system-metric(touch-enabled)
  • :-moz-system-metric(windows-default-theme)
• The following proprietary Mozilla media features are no longer available to web content (bug 1396066):
  • -moz-color-picker-available
  • -moz-is-glyph
  • -moz-mac-graphite-theme
  • -moz-mac-yosemite-theme
  • -moz-os-version
  • -moz-overlay-scrollbars
  • -moz-physical-home-button
  • -moz-scrollbar-end-backward
  • -moz-scrollbar-end-forward
  • -moz-scrollbar-start-backward
  • -moz-scrollbar-start-forward
  • -moz-scrollbar-thumb-proportional
  • -moz-swipe-animation-enabled
  • -moz-windows-accent-color-in-titlebar
  • -moz-windows-classic
  • -moz-windows-compositor
  • -moz-windows-default-theme
  • -moz-windows-glass
  • -moz-windows-theme
• The proprietary Mozilla :-moz-styleeditor-transitioning pseudo-class is no longer available to web content (bug 1396099).

• The non-standard Date.prototype.toLocaleFormat() method has been removed (bug 818634). See Warning: Date.prototype.toLocaleFormat is deprecated for more information and migration help.
• The non-standard and deprecated Object.prototype.watch() and unwatch() methods have been removed and will no longer work (bug 638054). Consider using setters and getters or proxies instead.
• The legacy Iterator protocol, the StopIteration object, the legacy generator functions and the non-standard Function.prototype.isGenerator() method have been removed. Use the ES2015 iteration protocols and standards-compliant iterators and generators instead (bug 1083482, bug 1413867, bug 1119777).
• The non-standard Array comprehensions and Generator comprehensions have been removed (bug 1414340).

• The proprietary moz-blob and moz-chunked-text values of the XMLHttpRequest.responseType property were removed completely in Firefox 58 (bug 1397145, bug 1397151, bug 1120171).
• The dom.abortController.enabled and dom.abortController.fetch.enabled prefs that controlled exposure of the Abort API functionality have now been removed, since those features are now enabled by default (bug 1402317).
• The proprietary mozSrcObject property was removed in Firefox 58 (bug 1183495). Use the standard HTMLMediaElement.srcObject property instead.

No changes.

• browserSettings
  • browserSettings.webNotificationsDisabled has been implemented (bug 1364942)
• browsingData
  • browsingData.localStorage now supports deleting localStorage by host (bug 1388428)
• pkcs11 API to manage security devices (Bug 1357391)
• privacy
  • first party isolation can now be toggled though firstPartyIsolate (bug 1409045)
  • resist fingerprinting pref can now be toggle through resistFingerprinting (bug 1397611)
• tabs
  • tabs.discard has been implemented (Bug 1322485)
  • isArticle, isInReaderMode properties of Tab implemented (Bug 1381992)
  • toggleReaderMode() method implemented (Bug 1381992)
  • openInReaderMode option of tabs.created implemented (Bug 1408993)
  • tabs.onUpdated now notifies when entering/exiting reader mode (Bug 1402921)
• theme
  • getCurrent() method to obtain current theme properties (Bug 1349944)
  • onUpdated method to receive WebExtension theme updates (Bug 1349944)
  • colors.bookmark_text now supported as alias of colors.toolbar_text (Bug 1412595)
  • colors.toolbar_top_separator, colors.toolbar_bottom_separator and colors.toolbar_vertical_separator implemented (Bug 1347190)
• webRequest
  • webRequest.onBeforeRequest now includes a "frameAncestors" parameter