Building Thunderbird

How to build and run Thunderbird.

Hardware Requirements

  • At least 4 GB of RAM. 8 GB or more is recommended. While you can build Thunderbird on older hardware it can take quite a bit of time to compile on slower machines with less RAM.

  • 30 GB of free space. The Thunderbird build can use up to 30-40GB of disk space to complete depending on your operating system.

  • Good internet connection for the initial source download.

Build Prerequisites

Depending on your Operating System you will need to carry out a different process to prepare your machine. So first complete the instructions for your OS and then continue following these build instructions.

Build Configuration

To build Thunderbird, you need a file named mozconfig in the root directory of the mozilla-central checkout that contains the option comm/mail enabled. If you do not already have this file, then you can create it with this line by doing this in the source/ directory:

echo 'ac_add_options --enable-project=comm/mail' > mozconfig

If you omit this line, the build system will build Firefox instead. Other build configuration options can be added to this file, although it's strongly recommended that you only use options that you fully understand. For example, to create a debug build instead of a release build, that file would also contain the line:

echo 'ac_add_options --enable-debug' >> mozconfig

Each of these ac_add_options entries needs to be on its own line.

For more info on configuration options, see the page Configuring build options. Note that if you use a MOZ_OBJDIR it cannot be a sibling folder to your source directory. Use an absolute path to be sure!


Before you start, make sure that the version you checked out is not busted. For hg tip, you should see green Bs on

After you have met the build prerequisites for your OS, the build is started in the source directory with:

./mach build

mach is our command-line tool to streamline common developer tasks. See the mach article for more.

Building can take a significant amount of time, depending on your system, OS, and chosen build options. Linux builds on a fast box may take under 15 minutes, but Windows builds on a slow box may take several hours.

Make Your Build Faster

Follow this guide to rely on sccache and other Tips for making builds faster.

Running Thunderbird

To run your build, you can use:

./mach run

There are various command line parameters you can add, e.g. to specify a profile.

Various temporary files, libraries, and the Thunderbird executable will be found in your object directory (under comm-central/), which is prefixed with obj-. The exact name depends on your system and OS. For example, a Mac user may get an object directory name of obj-x86_64-apple-darwin10.7.3/.

The Thunderbird executable in particular, and its dependencies are located under the dist/bin folder under the object directory. To run the executable from your comm-central working directory:

  • Windows: obj-.../dist/bin/thunderbird.exe

  • Linux: obj-.../dist/bin/thunderbird

  • macOS: obj-.../dist/

Update and Build Again

To pull down the latest changes, in the mozilla directory run the following commands:

hg pull -u
cd comm
hg pull -u
cd ..

or to do it via one command:

hg pull -u; (cd comm; hg pull -u)

Then just run the ./mach build command detailed in the Building instructions above. This will only recompile files that changed, but it may still take a long time.


To build after changes you can simply run:

./mach build

Rebuilding Specific Parts

If you have made many changes, but only want to rebuild specific parts, you may run the following commands.

C or C++ Files:

./mach build binaries

JavaScript or XUL Files (Windows Only):

./mach build path/to/dir

Replace path/to/dir with the directory with the files changed.

This is the tricky bit since you need to specify the directory that installs the files, which may be a parent directory of the changed file's directory. For example, to just rebuild the Lightning calendar extension:

./mach build comm/calendar/lightning

Last updated