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Release Notes tell you what’s new in Firefox. As always, we welcome your feedback. You can also file a bug in Bugzilla or see the system requirements of this release.

Firefox Developer Edition — English (US)

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Firefox Developer Edition — English (US)

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Firefox Developer Edition

November 10, 2014

Version 35.0a2, first offered to Firefox Developer Edition channel users on November 10, 2014

For more information about Developer Edition please see this MDN article and also this post.


  • Developer Edition application launcher icon

  • Developer Edition theme

  • Toolbox launcher

  • Valence - an automatically installed add-on provides debugger support for Safari on iOS

  • Developer Edition uses its own profile, can be disabled (see bug 1086936)

  • Ambient update notification

  • Built-in support for H264 (MP4) on Mac OS X Snow Leopard (10.6) and newer through native APIs

  • Improved handling of dynamic styling changes to increase responsiveness


  • Support for inspecting ::before and ::after pseudo elements

  • WOFF2 fonts are now supported (on Aurora and Nightly)

Developer Information

Web Platform

  • Changed JavaScript 'let' semantics to conform better to the ES6 specification

  • Resource Timing API implemented

  • CSS filters enabled by default

  • WebSocket now available in Web Workers


  • Firebug theme is not compatible with Developer Edition theme (see Issue 177)