Firefox 14 for developers

Firefox 14 shipped on July 17, 2012. This article lists key changes that are useful for not only Web developers to know about, but also Firefox and Gecko developers as well as add-on developers.

Changes for Web developers


  • The <progress> element is no longer incorrectly classified as a form element, and therefore no longer has a form attribute.
  • The default modifier keys for the accesskey of HTML contents on Mac are changed to Control+Option. This is the same as WebKit-based browsers on Mac.


  • input events are fired also on editing host element of contenteditable editor and root element of designMode editor.
  • DOMException.code is now deprecated per latest DOM Level 4 specification.
  • The Range.insertNode() method now works correctly when used on collapsed ranges.
  • The MozBlobBuilder interface has been deprecated in favor of the constructor on Blob. If you use MozBlobBuilder you'll see a warning message in the Web Console.
  • The Blob() constructor is now available to workers (bug 736686).
  • Support for the Mutation Observers has been landed. It is designed as a replacement for the Mutation Events in DOM3, which has a number of issues regarding performance.
  • The HTMLImageElement interface's x and y properties were removed in Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4) but restored in this release for compatibility reasons.
  • The Document methods execCommandShowHelp() and queryCommandText(), which never did anything, have been removed.
  • The GeoPositionAddress interface, an obsolete part of the Geolocation API, has been removed.
  • localStorage/sessionStorage now correctly return undefined instead of null for undeclared keys through property access.ff
  • The ImageData object has been implemented (bug 550309).
  • Attributes and methods related to child nodes on Attr interface where obsoleted (bug 737122).


  • The text-transform and font-variant CSS properties have been fixed to correctly handle the iİ and ıI Turkic-specific case pairs.
  • The Dutch IJ digraph is now correctly handled by text-transform: capitalization. Similarly the Greek letter Σ, which has two lowercase forms, σ and ς, is now correctly handled by text-transform: lowercase.
  • Support for the skew() function has been removed from transform property, as it has been removed from the draft standard.
  • The syntax for border-image has been updated to match the latest revision of the specification; it no longer accepts a trailing slash ("/").


No change.


  • The syntax of the statusline action type on <maction> elements has been adjusted to follow the MathML specification.


  • Gecko now supports the new HTTP 308 Permanent Redirect status code. As Gecko doesn't make a distinction between permanent and temporary redirects, it behaves like the 307 Temporary Redirect status code, as it forbids the user agent from changing the HTTP method used between the two requests (POST will stay POST, GET will stay GET).

Changes for Mozilla and add-on developers

JavaScript code modules


  • Added a keyboard shortcut to toggle commenting for the current selection (Ctrl-/ or Cmd-/ on Mac OS X).
  • Added the Ctrl-[ and Ctrl-] keyboard shortcuts for moving the text input position to the beginning and end of the current block.
  • Added the new getLineStart() and getLineEnd() methods.


  • Added the new fullscreenbutton attribute to the window element; setting this to true adds a button to the window's chrome to enable full screen mode.



  • Dictionary names are now parsed as full BCP 47 language tags (bug 730209, bug 741842). Developers are encouraged to not hard-code the name of their language in their dictionary names.

See also

Document Tags and Contributors

 Last updated by: Sebastianz,