Build Pale Moon on Windows

These instructions are for building Pale Moon 28.* (using UXP)


  • Microsoft Visual Studio 2015 (Community Edition (free) or Pro/Paid version -- Express won't work)
We will assume here you are using the Community Edition.
  • MozillaBuild 2.0, 2.1 or 2.2
  • At least 4 GB Ram (8 GB or more recommended)
  • Plenty of free disk space
  • At least Windows 7 64-bit

Prerequisite caveats

  • To get Visual Studio 2015 CE you need a Developer Account (simply a Microsoft account). Microsoft will try to push VS 2017 on you but that will not work. You must get 2015 from the "previous versions" part of the site.
  • Launch VS2015 after installation to initialize the environment, start the IDE and get the latest updates. Launch after updating to finish up the update, after which you can close the IDE. For x64 builds, make sure you install the x64 build tools.
    (Note: You will be asked to register with Microsoft when launching it the first time; simply log in with your developer account in the IDE and you're set.)
  • Make sure you install the correct components for "C++ development"; other languages are not necessary and not installing them will save you (heaps of) disk space.

Getting the Source

Download the source from here or clone with git
Make sure you unpack/clone to a path that does not contain spaces, e.g. c:\palemoon-source to prevent build system issues.

If you cloned the git repo be sure to switch to the desired relbranch. Since the repo contains multiple applications and trunk may be unstable, this is important.

This source tree will contain everything needed for both x86 and x64 builds of Pale Moon (they share the same release source code).

Build Instructions


Create a file called .mozconfig in the source folder you unpacked the source in.
(Yes, that is {dot}mozconfig -- don't omit the . at the start. Also make sure it's not .mozconfig.txt or something crooked like that. If you are hiding extensions of known file types, fix that first in folder options because it's a PITA when trying to do this kind of thing)

Make sure it contains at least the following for a close-to-official build:

For x86 (32-bit):

ac_add_options --enable-application=palemoon
ac_add_options --enable-optimize="-O2"
ac_add_options --enable-jemalloc
ac_add_options --disable-eme
ac_add_options --disable-webrtc
ac_add_options --enable-devtools
ac_add_options --disable-gamepad
ac_add_options --disable-parental-controls 
WIN_UCRT_REDIST_DIR="C:/Program Files (x86)/Windows Kits/10/Redist/ucrt/DLLs/x86"

For x64 (64-bit):

ac_add_options --enable-application=palemoon
ac_add_options --enable-optimize="-O2"
ac_add_options --enable-jemalloc
ac_add_options --disable-eme
ac_add_options --disable-webrtc
ac_add_options --enable-devtools
ac_add_options --disable-gamepad
ac_add_options --disable-parental-controls 
WIN_UCRT_REDIST_DIR="C:/Program Files (x86)/Windows Kits/10/Redist/ucrt/DLLs/x64"

To speed up the build you probably want to exclude building automated tests (which aren't actively used and may not always build properly)

ac_add_options --disable-tests

Note: LESS IS MORE! There are some pre-made build configs out there that have a lot of options listed, often with insane resulting build configurations. **Do not use those** and stick to the instructions here.


  • Go to C:\mozilla-build (or wherever you extracted to mozilla build tools) and run start-shell-msvc2015.bat
This will open a UNIX-like shell with the compile environment set up for Visual Studio 2015 with a 32-bit target. Please do not use the -x64 batch file even if you are on a 64-bit operating system when building x86.
The -x64 batch file is for launching a 64-bit build environment and building a 64-bit browser. So for creating an x64 build of Pale Moon, run start-shell-msvc2015-x64.bat
  • In the shell, cd to your pale moon source directory, e.g.
cd /c/palemoon-source
if you installed the source in C:\palemoon-source
  • Start the build:
./mach build
  • Be patient. Building will take a long time. Your PC will be fully occupied compiling and linking the browser (you can expect 100% CPU usage throughout and lots of memory use - provide ample cooling) and you should not be using it for anything else that is intensive at this time. Especially memory-intensive applications should be avoided because it can cause issues with the linker (memory fragmentation) resulting in a very unstable browser.

Important note: before you start building, make sure to exclude the source and target folders from antivirus software or it will severely slow down the build process or may even break it entirely (due to file locks). Either completely disable real-time/on-access scanning before building, or make specific exclusions for your working folders.


After building is completed, you can take the resulting binaries for a test run in the object directory directly (see the on-screen instructions at the end of the build process) but it will not be complete yet. You need to strip and package the browser to integrate additional code, pack up the omnijar files, and have a ready-to-use browser. You do this by running

./mach package

This will create a properly packaged .zip file in your object folder under the Pale Moon source folder. e.g.:
C:\palemoon-source\obj-i686-pc-mingw32\dist\palemoon-{version} (for x86)

Generating the installer

If you want to build a self-extracting installer, similar to the off-line installers offered in official builds, you will have to do give the following command:

./mach installer

This will create a self-extracting installer in your object folder under the Pale Moon source folder. e.g.:
C:\palemoon-source\obj-i686-pc-mingw32\dist\install\sea\palemoon-{version}.en-US.win32.installer.exe (for x86)

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