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The Mozilla source code can be obtained either by downloading a source archive or by using a Mercurial (source control) client. If you are just starting out or you want to build a particular Mozilla product release, downloading a source archive is recommended. Otherwise, get the Mozilla Source Code Via Mercurial (for Firefox) or Comm-central Source Code via Mercurial (for Thunderbird, SeaMonkey and Firefox). If you want to browse the source instead of downloading it, read Viewing and searching Mozilla source code online.

Before attempting a build, please review the system requirements and build instructions.


Licensing information for the source code is on our licensing page.



The source code for a release can be found on the Archive server in the "source" subdirectory of the release you want to acquire. The directory structure on the server is as follows:

where the names in italics mean the following:

  • PROJECT - The project name, such as firefox or thunderbird.

  • RELEASE - The release, such as 53.0.3.

For example, the source code for Firefox release 53.0.3 can be found at the following URL:

The easiest way to find the source code of the release you want is to start at and navigate your way to it, bearing in mind the directory structure described above. To navigate the archive server use a browser like Firefox.

Note: Some projects do not provide source code for download, for example.bonsai In this case, you should use CVS (if possible). Specific versions of the applications are accessible with specific CVS Tags.

The entire source tree is not available for download over HTTPS.


Source tarballs of the nightly snapshots are not provided.


Source code is packaged as bzipped tarballs. This means that you must have tar along with bzip2 installed, since the -j flag in the commands listed below means the archive is first being unpacked with. bzip2 To unpack a tarball from a Unix-like shell (or the Cygwin shell), type:

tar -xjf <source-file.tar.bz2>

Or, if you want to see the files extracted,

tar -xjvf <source-file.tar.bz2>
Note for Windows users: using WinRAR or WinZip to unpack source archives will not work. WinZip does not support *.bz2 files, and the archive contains zero-length files which are not unpacked properly. For windows, try 7-zip software.

If the files end with .tar.xz extension unpack via tar (GNU tar version 1.29+):

tar xfJ firefox-RELEASE.source.tar.xz

Or alternatively, you may need xz (from

xz -d firefox-RELEASE.source.tar.xz

And then tar to extract the archive:

tar xf firefox-RELEASE.source.tar