This is an archived page. It's not actively maintained.

Gecko SDK

The Gecko SDK, also known as the XULRunner SDK, is a set of XPIDL files, headers and tools to develop XPCOM components which can then in turn e.g. be accessed from XUL using JavaScript.

Note that in order to develop such components, you do not need the full sources of e.g. Firefox, since you do not access parts of the front end from within a component. Furthermore, since a component contains basic functionality, it is intended to run with every product of the Mozilla platform. Therefore it makes no sense to use a particular product to build general functionality. That's the reason why the Gecko SDK was devised.

Do not confuse the Gecko/XULRunner SDK with XULRunner itself. The Gecko SDK is a collection of header files and tools used to develop general XPCOM components which add functionality to the existing platform, whereas XULRunner is a framework which can be used to run standalone or embedded applications based on the Mozilla framework.

The Gecko SDK contains all of the necessary tools and headers for making scriptable NPAPI plugins including the xpidl compiler/linker and the latest npapi.h.

Get the SDK


There is no need to download or rebuild the Gecko SDK corresponding to security updates of Mozilla (e.g., Mozilla 1.7.3) since the headers and glue libs in the Gecko SDK are usually not changed as a result of security updates. You do have to get and distribute the newest Gecko components (gklayout.dll etc.), though.


For Gecko versions before 2.0, you should choose the Gecko SDK version for the earliest version of Mozilla you wish to target.  For Gecko versions 2.0 and higher, you must recompile your component for each release as cross-version compatibility is no longer supported.

In addition to the below versions, you can find other versions (including Beta) here: Xulrunner Releases (files include "sdk" in the name).  The SDK follows the same release schedule as Firefox/Thunderbird.  Once the SDK enters Beta, it is suitable for building extensions; your component should work with release builds of the SDK without any modifications.  Due to the Rapid Release process, it may be a good idea to target the SDK in Beta.

Download Link Latest Gecko (Latest Firefox) Gecko 1.9.2 (Firefox 3.6) Gecko 1.9.1 (Firefox 3.5) Gecko 1.9 (Firefox 3.0) Gecko 1.8 (Firefox 1.5 and 2.0)
Windows Download Download Download Download Download
Mac x86_64 Download N/A N/A N/A N/A
Mac i386 Download Download Download Download N/A
Mac ppc N/A Download Download Download Download
Linux x86_64 Download N/A N/A N/A N/A
Linux i686 Download Download Download Download Download

The SDK is not officially released for other platforms; if you need it, you will probably need to build it yourself.

Note: You can subscribe to a calendar of the Firefox release schedule. Also, you can view the schedule on the Web.

Unpack the SDK tarball to some suitable location.

Issues with the OS X SDK

If you need to use the xpidl utility to compile IDL files on OS X, it's likely that you will receive a strange error when running the tool that looks something along the lines of this:

dyld: Library not loaded: /opt/local/lib/libintl.3.dylib
  Referenced from: /Users/varmaa/xulrunner-sdk/bin/./xpidl
  Reason: image not found
Trace/BPT trap

Unfortunately, this is caused by a problem with the SDK build process which cannot currently be resolved (see Bugzilla bug #430274). To get around it, you'll need to first install MacPorts as outlined in the Mac OS X Build Prerequisites and install libidl with it. On 64-bit versions of Mac OS X, you'll need to install libidl with the +universal flag.

Once that's done, you should perform the following command:

ln -s /opt/local/lib/libintl.8.dylib /opt/local/lib/libintl.3.dylib

This should fix the problem.

Building the SDK

To build the SDK, you should build XULRunner (the Gecko SDK is built as part of the XULRunner build process, which is why it's sometimes called the XULRunner SDK). See the Build Documentation for complete details. After the XULRunner build is complete running make sdk from your object directory will create a package of the sdk in dist.

Contents of the SDK

The SDK contains the following:

  • 1.9.2
  • IDL files for frozen interfaces (under idl/)
  • Header files for frozen interfaces, XPCOM functions, and NSPR functions (under include/)
  • Import libraries or shared libraries (under lib/)
  • Static utility libraries (under lib/)
  • Various tools (under bin/)

For more information about safely linking XPCOM components using the XPCOM "glue" library, see XPCOM Glue.

Using the Mozilla Build System with the SDK

It's possible to use the Mozilla Build System with the SDK. This can be done by downloading the source code for Firefox and using the --with-libxul-sdk option to configure.


  • static xpidl.exe (non-official) If you are looking for a static linked xpidl.exe, you can download here.
  • Mac Intel Gecko 1.8 SDK The official Mac 1.8 SDK is a ppc version. This is an unofficial intel build.