Firefox 52 for developers

Firefox 52 was released on March 7, 2017. This article lists key changes that are useful not only for web developers, but also Firefox and Gecko developers as well as add-on developers.

Changes for Web developers

Developer Tools

All devtools bugs fixed between Firefox 51 and Firefox 52.



New features

CSS Grids

Changes and removals

  • Unprefixed multi-column properties (and added back -moz prefixed versions as aliases, for now) (bug 1300895).
  • Stopped wrapping abspos children of flex container in anonymous flex items(bug 1269045).
  • Implemented grid container baselines (bug 1151204).
  • Removed <flex> min-sizing from the style system (bug 1305244).
  • Remove preference layout.css.masking.enabled (bug 1308239).
  • The proprietary -moz-images-in-menus and -moz-images-in-buttons media types have been removed (see bug 1302157).
  • Removed -moz-use-text-color value from color properties; use currentcolor instead (bug 1306214).
  • [css-grid] 'max-width' set on grid item causes text to overflow (bug 1330380).


New features

Changes and removals



Changes and removals

Service Workers and Fetch

  • The Headers.getAll() method has been removed, and Headers.get() now retrieves all values of the specified header, not just the first one (see bug 1278275). This is in accordance with the latest Fetch API spec updates.

Web Audio API


  • When an ICE connection is temporarily disrupted, the RTCPeerConnection.iceConnectionState property now gets set to "disconnected"; this indicates a transitory failure that may resolve itself shortly, with the connection returning to the "connected" state afterward (bug 852665).
  • The MediaDevices.ondevicechange event handler and corresponding devicechange event, which were implemented but disabled by default on Mac only in Firefox 51, have been implemented on Windows and Linux and are now enabled by default on all platforms.
  • The property is now supported. This read-only Boolean property indicates whether or not at least one track on the stream is currently playing.
  • Prior to Firefox 52, the MediaStreamTrack.stop() method could only stop local tracks (that is, tracks obtained through getUserMedia()). Now a variety of tracks can be stopped, including those on a MediaStream associated with a WebRTC connection, Web Audio API stream, or CanvasCaptureMediaStream.
  • Previously, changing a TextTrack's mode repeatedly during a single pass through the Firefox event loop would result in multiple change events being delivered to the TextTrackList specified by the parent media element's textTracks property. Now these changes are consolidated into one event (bug 882674).


  • The MediaError objects specified in HTMLMediaElement.error when an error occurs handling an <audio> or <video> element now include a message property, which provides a specific description of the error which occurred. This string offers details particular to this exact error occurrence, offering insight into why things went wrong (bug 1299072). This field has been included in Firefox nightly builds since Firefox 51, but is now available in all builds, up to and including release.

Other APIs



  • SVG documents are now represented using the XMLDocument interface instead of SVGDocument. This is a change made in the SVG 2 specification.


  • When login pages (i.e those containing an <input type="password"> field) are created so that they would be submitted insecurely, Firefox displays an in-context warning message below the password field to warn users (bug 1319119). Autofill is also disabled on insecure login forms (bug 1217152). See Insecure passwords for more details.
  • Support for SHA-1 SSL certificates has been removed; navigating to a secure page that uses a SHA-1 certificate will now result in an Untrusted Connection error (bug 1330043).


All NPAPI plugin support except Flash has been dropped (see Plug-in support has been dropped other than Flash for more details). Flash usage is also set to be phased out in the future.

Changes for add-on and Mozilla developers


New APIs:



See also

Older versions

Document Tags and Contributors

 Last updated by: chrisdavidmills,