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Firefox 41 was released on September 22, 2015. 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


All devtools bugs fixed between Firefox 40 and Firefox 41: note that many of these bugs, especially those relating to the performance tools, were uplifted to Firefox 40.





HTML Editing API


Web Crypto

Canvas API

Service Workers


  • The failIfMajorPerformanceCaveat WebGL context attribute has been added and can be set when creating a WebGL context with HTMLCanvasElement.getContext() to indicate if a context creation should fail if the system performance is low (bug 1164970).


  • Firefox no longer offers a default STUN server to be used if none are specified when constructing a new RTCPeerConnection. You'll need to provide one in order to successfully establish a WebRTC connection.



New default and fallback font handling

Mathematical formulas require special fonts. So far, these fonts were hard-coded in the mathml.css user agent stylesheet (which sets the font-family on <math> tag) and in the preference option font.mathfont-family (which sets the fallback fonts to use for stretchy and large operators). Firefox 41 introduces, an internal x-math language that is automatically set on the <math> tag as well as corresponding preference options (e.g. The user agent stylesheet now sets font-family to serif on the <math> tag and the preference option font.mathfont-family is replaced with  All platforms now essentially use the same list of fallback fonts, with "Latin Modern Math" as first one. The default/fallback fonts can be configured from the standard per-language font preference menu. For more details, see bug 947654 and bug 1160456.


  • Site icons (favicons, shortcut icons) now support SVG (bug 366324).


  • The media.autoplay.enabled preference now also apply to untrusted invocations too, that is calls from non-users activated scripts (bug 659285).


  • The X-Content-Duration header is no longer supported (bug 1160695).
  • Draft versions of the HTTP/2 protocol are no more supported (bug 1132357).


  • The CSP 1.1 manifest-src directive is now supported (bug 1089255).
  • Previous versions of Firefox incorrectly expected the Content Security Policy referrer directive's value origin-when-cross-origin to be spelled origin-when-crossorigin. This has been corrected to include the missing dash character.

Changes for add-on and Mozilla developers


No change.

JavaScript code modules

No change.



No change.


See also

Older versions

Document Tags and Contributors

 Last updated by: Sheppy,