Firefox 53 for developers

Firefox 53 was released on April 19, 2017. This article lists key changes that are useful not only for web developers but also for 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 (Firefox bug 1319667).
  • [css-grid] Fixed: align-self/justify-self:stretch/normal doesn't work on <table> grid items (Firefox bug 1316051).
  • Fixed: clip-path: circle() with large reference box and percentage radius does not render correctly (Firefox 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 Firefox 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 (Firefox 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 (Firefox bug 1333323).

Media elements

Web Audio API




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 (first enabled by default in Firefox 49) can no longer be disabled. See Firefox bug 1271549.
  • The mozapp attribute of the <iframe> element /HTMLIFrameElement interface has been removed — this was used to enable a Firefox OS app to be embedded in a mozilla-prefixed Browser API <iframe> (Firefox bug 1310845).
  • The HTMLIFrameElement.setInputMethodActive() method and InputMethod interface (used to set and manage IMEs on Firefox OS apps) has been removed (Firefox bug 1313169).





Changes for add-on and Mozilla developers


New APIs:

Enhanced APIs:

JavaScript code modules

  • The asynchronous [AddonManager APIs]((/en-US/docs/Mozilla/Add-ons/Add-on_Manager/AddonManager) now support Promises as well as callbacks (Firefox bug 987512.

Older versions