Firefox 33 for developers

Firefox 33 was released on October 14, 2014. 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


  • Event listeners popup
  • @media sidebar
  • Add new rule
  • Edit keyframes
  • Cubic bezier editor
  • Transform highlighter
  • Persistent disable cache
  • New Commands
  • Editor preferences
  • WebIDE

For details please see the hacks post. Special thanks to the 33 contributors that added all the features and fixes in this release.


  • Implemented @counter-style rule (bug 966166).
  • Unprefixed ethiopic-numeric, persian, arabic-indic, devanagari, bengali, gurmukhi, gujarati, oriya, tamil, telugu, kannada, malayalam, thai, lao, myanmar, khmer, cjk-heavenly-stem, cjk-earthly-branch in list-style-type (bug 985825 and bug 1063856).
  • Added support for mongolian, disclosure-open and disclosure-closed counter styles in list-style-type (bug 982355 and bug 1063856).
  • Fixed CSS animations with empty keyframes rule so they also dispatch events (bug 1004377).
  • Added support for rebeccapurple, a new <color> name defined in CSS Colors level 4 (bug 1024642).
  • Our experimental implementation of CSS Fonts Level 3 progresses. Its activation is governed by the layout.css.font-features.enabled preference, enabled by default in Nightly. Newly implemented features are:


  • Added the experimental support for <picture> element (bug 870022), behind the dom.image.picture.enabled preference (off by default).
  • The <label>, especially without a for attribute, doesn't apply anymore to a <input type=hidden> field (bug 597650). The previous behavior wasn't spec compliant.
  • The link annotation noreferrer has been implemented on <a> elements. <a rel="noreferrer"> will not include the URL of the referrer in the HTTP request sent to fetch it (bug 530396). Note that this work only for in-page links, not for linked clicked via the UI, like via contextual menus.
  • On Android, support for two new values for the name attribute of <meta> has been added: msapplication-TileImage and msapplication-TileColor (bug 1014712). Example:
    <meta name="msapplication-TileImage" content="images/benthepcguy-144.png" />
    <meta name="msapplication-TileColor" content="#d83434" />





No change.



  • EXT_blend_minmax is now exposed. It extends blending capabilities by adding two new blend equations: producing the minimum or maximum color components of the source and destination colors (bug 973815).


Changes for add-on and Mozilla developers

Add-on SDK



GitHub commits made between Firefox 32 and Firefox 33. This will not include any uplifts made after this release entered Aurora.

Bugs fixed between Firefox 32 and Firefox 33. This will not include any uplifts made after this release entered Aurora.

Older versions