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



New features

CSS Grids

Changes and removals


New features

Changes and removals



Changes and removals

  • The Firefox OS APIs that deal with managing phone calls (Contacts, MobileConnection, Icc, etc.) have been removed (Firefox bug 1311206).
  • The Firefox OS Identity interface has been removed (Firefox bug 1309030).
  • The Firefox OS Voicemail API (MozVoicemail, MozVoicemailEvent, MozVoicemailStatus, Navigator.mozVoicemail) has been removed (Firefox bug 1309723).
  • The Firefox OS Cell Broadcast API (MozCellBroadcast, MozCellBroadcastEvent, MozCellBroadcastMessage, Navigator.mozCellBroadcast) has been removed (Firefox bug 1306772).
  • The Firefox OS TV broadcast-related APIs have been removed (Firefox bug 1306778).
  • The Firefox OS FM Radio API (FMRadio, Navigator.mozFMRadio) has been removed (Firefox bug 1306779).

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 Firefox 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 (Firefox bug 852665).
  • The MediaDevices.devicechange_event event and its corresponding handler, 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 (Firefox 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 (Firefox 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 (Firefox bug 1319119). Autofill is also disabled on insecure login forms (Firefox 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 (Firefox bug 1330043).


All NPAPI plugin support except Flash has been dropped. Flash usage is also set to be phased out in the future.

Changes for add-on and Mozilla developers



  • nsIDroppedLinkHandler.dropLinks method and nsIDroppedLinkItem interface have been added to handle dropping multiple items (Firefox bug 92737).


  • tabbrowser.loadTabs(uris, params) method overload has been added (Firefox bug 92737).
  • browser.droppedLinkHandler function signature has been changed (Firefox bug 92737).

Older versions