Firefox 53, based on Gecko 53, will ship in April 2017. This article provides information about the changes in this release that will affect developers. Nightly builds of what will become Firefox 53 are currently available on the Developer Edition 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 53.

Items listed here are tentatively slated for Firefox 53; however, they may be held for a future release if testing shows they're not ready by the time Firefox 53 is due to ship. Please keep an eye on this page to stay up to date on the plans for Firefox 53.

Changes for Web developers

Developer Tools


New features

Other changes

  • Enable mask longhands on SVG elements (bug 1319667).
  • [css-grid] Fixed: align-self/justify-self:stretch/normal doesn't work on <table> grid items (bug 1316051).
  • Fixed: clip-path: circle() with large reference box and percentage radius does not render correctly (bug 1324713.
  • When applying a text-transform value of uppercase to Greek text, the accent on the disjunctive eta (ή) is no longer removed (see bug 1322989).
  • <input> elements of type checkbox and radio with -moz-appearance: none; set on them can now be styled with significantly more CSS properties (bug 418833, bug 1320732).
  • The availability of the contents value of display was controlled through the layout.css.display-contents.enabled pref. In Firefox 53 this pref has been removed altogether, so the value will always be available and can no longer be disabled (bug 1295788).




Workers and service workers


Audio, video, and media

Media elements

Web Audio API



  • Gecko now has a pref available in about:config to allow users to set their default Referrer-Policy network.http.referer.userControlPolicy (bug 1304623). Possible values are:
    • 0 — no-referrer
    • 1 — same-origin
    • 2 — strict-origin-when-cross-origin
    • 3 — no-referrer-when-downgrade (the default)
  • Support for Next Protocol Negotiation (NPN) has been removed in favour of Application-Layer Protocol Negotiation (ALPN) — see bug 1248198.


Removals from  the web platform


  • The dom.details_element.enabled pref — which controlled enabling/disabling <details> and <summary> element support in Firefox — has now been removed from about:config. These elements (which were first enabled by default in Firefox 49) can no longer be disabled. See bug 1271549.




Changes for add-on and Mozilla developers


New APIs:

Enhanced APIs:

JavaScript code modules

See also

Older versions

Document Tags and Contributors

 Last updated by: chrisdavidmills,