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Firefox 53 was released on April 19, 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

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).
  • 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


  • Beginning in Firefox 53 for Android, decoding of media is handled out-of-process for improved performance on multi-core systems (bug 1333323).

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 favor of Application-Layer Protocol Negotiation (ALPN) — see bug 1248198.
  • The Large-Allocation HTTP header is now available by default, and no longer hidden behind a pref (bug 1331083).


Removals from the web platform






Changes for add-on and Mozilla developers


New APIs:

Enhanced APIs:

JavaScript code modules

See also

Older versions

Tag del documento e collaboratori

Hanno collaborato alla realizzazione di questa pagina: wbamberg, chrisdavidmills, Sebastianz, yisibl, myakura, Sheppy, craue, fscholz, claudepache, teoli, kmaglione, arai
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