Firefox 54 for developers

Firefox 54 was released on June 13, 2017. This article lists key changes that are useful for web developers.

Changes for Web developers

Developer Tools

  • The network request summary now includes the amount of data actually transferred ("transferred size"), as does the performance analysis view (Firefox bug 1168376).
  • The network request headers view now links to the related documentation on MDN (Firefox 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 (Firefox bug 1335555).
  • Support has been added for the VP9 codec in encrypted streams using Clear Key and Widevine (Firefox 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 (Firefox bug 1176382). This blog post explains the feature in more details.

Removals from the web platform



  • 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 Firefox bug 1340655 for further information.

Older versions