Firefox 39 for developers

Firefox 39 was released on July 2, 2015. 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

Highlights:

All devtools bugs fixed between Firefox 38 and Firefox 39.

CSS

  • Support of the <string>Ā type on list-style-type, as well as its shorthand property list-style has been implemented (bugĀ 1144607).
  • CSS Scroll Snapping has been implemented (bugĀ 945584 and bugĀ 1138658).
  • Cascading of CSS Animations and CSS Transitions has been rewritten to match the latest specification (bugĀ 1125455).
  • Support for vertical scripts, with the writing-mode is now turned on by default on Nightly and Developer Edition, but not on Firefox Beta and Firefox Release (bugĀ 1099032). Note that implementation is not yet complete and some widgets, like tables, will not obey to all values.
  • CSS filter acts like position: relative + overflow: hidden (bugĀ 1125767).

HTML

  • A new ARIA role, switch, is now supported (bugĀ 1136563).
  • Support for <link rel="preconnect"> allowing to anticipate a future connection without revealing any information has been implemented (bugĀ 1135160).

JavaScript

Interfaces/APIs/DOM

MathML

No change.

SVG

No change.

Audio/Video

No change.

Miscelleanous

Networking

Security

No change.

Changes for add-on and Mozilla developers

No change.

See also

Older versions