Firefox 24 for developers

Changes for Web developers


  • The two values -moz-zoom-in and -moz-zoom-out of the cursor property have been unprefixed to zoom-in and zoom-out (Firefox bug 772153).
  • To match the specification, the keywords not, only, and, and or cannot be used as media types anymore (Firefox bug 757554).


  • The <track> element has been implemented behind the media.webvtt.enabled preference, and is disabled by default. (Firefox bug 833385).



Developer Tools

  • The Network inspector now lets you filter by content type (CSS/image/font etc.) and see the relevant size and load times.
  • The Devtools options panel to the left lets you disable/enable JavaScript temporarily.
  • Extension developers may use the new Browser Console for Chrome-level scripts (Replaces Error Console).
  • The source map syntax has been changed to use //# instead of //@ (Firefox bug 870361).


  • The dir attribute for controlling directionality of formulas on e.g. <math> or <mrow> elements is now equivalent to using the direction CSS property.
  • The equal sign ("=") is now stretchable.
  • The "updiagonalarrow" value for the notation attribute on <menclose> elements has been added.

Changes for add-on and Mozilla developers

  • Doc Shells have now the allowMedia attribute to disable media playing (Firefox bug 759964).
  • Sherlock search plugins in the application directory or profile won't be loaded anymore (Firefox bug 862143).

See also

Older versions