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

Changes for Web developers

Developer Tools

HTML

No changes.

CSS

SVG

No changes.

JavaScript

APIs

New APIs

DOM

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

HTTP

Security

No changes.

Plugins

No changes.

Other

Removals from the web platform

HTML

  • 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).

CSS

JavaScript

APIs

SVG

No changes.

Changes for add-on and Mozilla developers

WebExtensions

  • browserSettings
  • browsingData
  • 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

See also

Older versions

Document Tags and Contributors

Last updated by: chrisdavidmills,