Firefox 28 for developers

Firefox 28, based on Gecko 28, will ship in March 2014. This article provides information about the changes in this release that will affect developers. Nightly builds of what will become Firefox 28 are currently available on the Nightly channel.

Note: Items listed here are tentatively slated for Firefox 28; however, they may be held for a future release if testing shows they're not ready by the time Firefox 28 is due to ship. Please keep an eye on this page to stay up to date on the plans for Firefox 28.

Want to help document Firefox 28? See the list of bugs that need to be written about and pitch in!

Changes for Web developers

Developer Tools



  • WebVTT has been switched on by default (bug 887978).


  • canPlayType('video/webm') should report “maybe” (bug 884275).

EcmaScript 6 (Harmony) implementation continues!


  • Add getElementById method on DocumentFragment, e.g. document.createDocumentFragment().getElementById() (bug 933193).
  • Implement DOM3 KeyboardEvent.repeat (bug 600117).
  • Implement the File constructor, e.g. new File(["foo"], "foo.txt") (bug 819900).


  • Support of mathvariant attribute (bug 114365).


No change.


Changes for addon and Mozilla developers

No change.

See also

Older versions


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