Firefox 54, based on Gecko 54, will ship in June 13, 2017. This article provides information about the changes in this release that will affect developers. Nightly builds of what will become Firefox 54 are currently available on the Nightly channel. Some experimental features whose release dates are uncertain or undecided are discussed on the page Experimental features in Firefox. Some features described there may be available in Firefox 54.

Items listed here are tentatively slated for Firefox 54; however, they may be held for a future release if testing shows they're not ready by the time Firefox 54 is due to ship. Please keep an eye on this page to stay up to date on the plans for Firefox 54.

Changes for Web developers

Developer Tools

  • The network request summary now includes the amount of data actually transferred ("transferred size"), as does the the performance analysis view (bug 1168376).
  • The network request headers view now links to the related documentation on MDN (bug 1320233).




Web Workers and Service Workers



Media Capture and Streams API

Web Audio API

Encrypted MediaExtensions API

  • The MediaKeySession.keySystem string has been removed from the specification, and as such we've taken it out of Firefox 54 (bug 1335555).
  • Support has been added for the VP9 codec in encrypted streams using Clear Key and Widevine (bug 1338064).
  • Previously, MSE was only allowed to use WebM/VP8 video if the system was considered "fast enough." Now playback of VP8-encoded webm/video media is always supported, regardless of system performance.


  • TCP ICE candidate support, originally added in Firefox 41, is now enabled by default. This allows the ICE layer to consider candidates that use TCP rather than the preferred UDP for transmission. This can be useful in environments in which UDP is blocked (bug 1176382). This blog post explains the feature in more details.

Removals from the web platform


  • Removed the -moz prefixed versions of isolate, isolate-override, and plaintext values for the unicode-bidi property (bug 1333675).


  • HTTP/1 Pipelining support has been removed in Firefox 54. Maintaining it as we make the move into a new world full of HTTP/2 and other substantial, standardized improvements to networking performance is not worthwhile given pipelining's compatibility and performance issues. The network.http.pipelining preference (as well as the other preferences that start with "network.http.pipelining") is now ignored. See bug 1340655 for further information.

See also

Older versions

Document Tags and Contributors

 Last updated by: fscholz,