Changes for Web developers

New in Firefox DevTools

  • The inspector now features autocompletion for CSS names and values.
  • The debugger now lets you "black box" script files, to prevent breakpoints from stopping in library code you're not interested in debugging.
  • The Profiler now has the ability to save and import profiling results. "Show Gecko Platform Data" is now an option in the Firefox developer tools options.
  • The Network panel has a right-click context menu, with copy and resend URL commands.
  • Numerous under-the-hood changes may make some rewriting necessary for addons that modify the DevTools.


  • The support for the keyword local as a value of the background-attachment CSS property has been added (bug 483446).
  • Support of a non-standard Mozilla-only media query to determine the operating system version has been added: -moz-os-version (bug 810399). The property is currently only implemented on Windows.
  • The -moz-osx-font-smoothing CSS property has been added (bug 857142).
  • Our experimental support for filter now supports the hue-rotate() functional notation (bug 897392). It is still preffed off by default.
  • page-break-inside: avoid is now working with the height of a block (bug 883676).


  • The srcdoc attribute of <iframe>, allowing the inline specification of the content of an <iframe>, is now supported (bug 802895).
  • When used with a "image/jpeg" type, the method HTMLCanvasElement.toBlob now accepts a third attribute defining the quality of the image (bug 891884).


EcmaScript 6 (Harmony) implementation continues!


  • The Web Audio API is now supported. An incomplete implementation was previously available behind a preference (bug 779297).
  • Some IME related keys on Windows are supported by KeyboardEvent.key (bug 865565), see the key name table for the detail.
  • Firefox for Metro now dispatches key events in the same way as the desktop version (bug 843236).
  • keypress event is no longer dispatched if preventDefault() of preceding keydown event is called (bug 501496), see the document of keydown event for the detail.
  • Renamed the Future interface to Promise (bug 884279).
  • The srcDoc property on the HTMLIFrameElement interface, allowing the inline specification of the content of an <iframe>, is now supported (bug 802895).
  • The createTBody() method on the HTMLTableElement interface, allowing to get its <tbody>, is now supported (bug 813034).
  • The Range.collapse() method toStart parameter is now optional and default to false, like defined in the spec (bug 891340).
  • Support of ParentNode interface on Document and DocumentFragment has been added (bug 895974).
  • The previousElementSibling and nextElementSibling have been moved to ChildNode allowing them to be called not only on a Element object but also on a CharacterData or DocumentType object (bug 895974).
  • The navigator.geolocation property has been updated to match the spec. It never returns null. When the preference geo.enabled is set to false, it now returns undefined (bug 884921).
  • The videoPlaybackQuality attribute on the HTMLVideoElement interface has been changed to the getVideoPlaybackQuality method. (bug 889205)
  • The non-standard GlobalObjectConstructor interface has been removed (bug 1089811). This interface was used to add arguments to the constructors of APIs that Firefox add-ons were exposing on the global object. This capability has been removed; note that at this time there's no replacement for this functionality.


No change.


No change.

See also

Older versions

Document Tags and Contributors

 Last updated by: kohei.yoshino,