Sometimes you might need to include changes you've made to Firefox in a new installer. This might be a policies.json file, AutoConfig changes or extensions. This document shows how to do that on Windows operating systems.

Step 1: Download installer

Download the installer file that you want to repackage. Make sure you download a full installer and not a stub installer. The stub installer is typically named “Firefox Installer.exe” whereas the full installer is named “Firefox Setup VERSION.exe”. You can download the Firefox Extended Support Release (ESR) full installer from https://www.mozilla.org/firefox/all/desktop-esr/ and the Firefox rapid release installer from https://www.mozilla.org/firefox/all/desktop-release/

Step 2: Unzip installer

Unzip the installer into a directory. You'll need to use 7-zip in order to unzip it.

7z x "Firefox Setup VERSION.exe"

Step 3: Make changes to Firefox

Make your changes to Firefox in the core subdirectory.

Step 4: Repackage files

Repackage Firefox by running this command in the directory where you unzipped Firefox.

7z a -r -t7z app.7z -mx -m0=BCJ2 -m1=LZMA:d24 -m2=LZMA:d19 -m3=LZMA:d19 -mb0:1 -mb0s1:2 -mb0s2:3

This will create a file called app.7z that contains the changes.

Step 5: Download utilities

Download the files 7zSD.Win32.sfx and app.tag, and save them in the same directory where the app.7z is located.

Step 6: Create installer

To concatenate the files and create the installer, run this command:

copy /B 7zSD.Win32.sfx+app.tag+app.7z our_new_installer.exe

The “/B” is very important! It tells copy that these are binary files, so it doesn’t add extra characters to the files.