Firefox 29 for developers

Firefox 29 was released on April 29, 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

Major changes include:

  • Vastly improved web console - Arrays are shown inline without clicking to bring up in the right inspector, window objects show their URL, etc.
  • Added the console API to Web Workers (bug 620935). Now you can log messages to the Web Console from Web Workers.
  • The Network Monitor tool now shows performance statistics using pie charts (Firefox bug 846601).
  • On the Inspector, preview tooltips of CSS transforms are now available (Firefox bug 726427).
  • DOM elements seen in the debugger and console can be removed or inspected directly, via the new buttons to the right of the variable listing.
  • A CSS source map is now supported by the Style Editor (Firefox bug 926014).
  • Autocompletion of CSS properties and values has been added to the Style Editor (Firefox bug 717369).

See the Mozilla Hacks blog post for details and other smaller changes.



  • <input type=color> and <input type=number> are available by default.
  • Support for the non standard <pre cols> has been removed, as well as the layout effect of <pre wrap>. Both effects can, and should, be achieved using CSS. (Firefox bug 949879)




No change.


No change.


  • The CSP 1.1 experimental hash-source directive has been implemented. The preference security.csp.experimentalEnabled should be set to true to enable this functionality (Firefox bug 883975).

Changes for add-on and Mozilla developers

  • Major Firefox theme changes affect most extensions that interact with the Firefox user interface.
  • nsISecurityCheckedComponent has been removed (Firefox bug 794943). Most consumers can remove nsISecurityCheckedComponent from their interface definition and they will continue to work.

Older versions