Firefox 51 for developers

Firefox 51, based on Gecko 51, will ship in January 2017. This article provides information about the changes in this release that will affect developers. Nightly builds of what will become Firefox 51 are currently available on the Nightly channel.

Changes for Web developers

Developer Tools

No change.

HTML

No change.

CSS

• Implemented inset() value for clip-path behind the preference layout.css.clip-path-shapes.enabled, defaulting to false (баг 1246762).
• [css-grid] Implement fit-content() value for <track-size> (баг 1281320).
• [css-grid] Percentage gutters are wrong calculated on grid containers with indefinite sizes (баг 1279182).
• [css-grid] Reject repeat() column tracks in <grid-template> when there's a grid template area string in the row part (баг 1282643).
• Implemented :indeterminate for <input type="radio"> (баг 885359).
• Implemented :placeholder-shown pseudo-class (баг 1069015).
• Unprefixed ::placeholder pseudo-element (баг 1069012).

JavaScript

• The ES2015 Symbol.toStringTag property has been implemented (баг 1114580).

Interfaces/APIs/DOM

DOM & HTML DOM

• Throttling in background tabs of timers created by Window.setInterval() and Window.setTimeout() was changed in Firefox 50 to no longer occur if a Web Audio API AudioContext is actively playing sound. However, this didn't resolve all scenarios in which timing-sensitive audio playback (such as music players generating individual notes using timers) could fail to work properly. For that reason, Firefox 51 no longer throttles background tabs which have an AudioContext, even if it's not currently playing sound.

Canvas

No change.

WebGL

No change.

IndexedDB

No change.

Service Workers

No change.

WebRTC

No change.

New APIs

No change.

Others

No change.

MathML

No change.

SVG

• Added tabindex attribute (баг 778654).
• Added href attribute obsoleting xlink:href (баг 1245751).

Audio/Video

• Add FLAC support (FLAC codec) in both FLAC and Ogg containers (баг 1195723).
• FLAC mimetype:
  • audio/flac
  • audio/x-flac
• FLAC in Ogg:
  • audio/ogg; codecs=flac
  • video/ogg; codecs=flac

HTTP

No change.

Networking

No change.

Security

No change.

Changes for add-on and Mozilla developers

Interfaces

No change.

XUL

No change.

JavaScript code modules

No change.

XPCOM

No change.

Other

• The Mozilla-specific Social API has been substantially changed (largely to remove APIs no longer used), as follows:
  • The MozSocial interface and the navigator.mozSocial property which supports it have been removed.
  • The Social Bookmarks API has been removed.
  • The Social chat functionality has been removed.
  • The Social Status API has been removed.
  • All of the social widgets, except for the Share panel, have been removed. This includes the social sidebar, flyover panels, and so forth.
  • All supporting user interface features and functionality for the removed APIs have been removed as well.
  • Social service provider manifest properties supporting the removed functionality are no longer supported.

See also

• Site Compatibility for Firefox 51

Older versions