Repackaging the Windows Installer
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.
Download the installer 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 full installer of Firefox Extended Support Release (ESR) from here and of rapid release from here.
Unzip the installer into a directory. You'll need to use 7-zip in order to unzip it.
7z x "Firefox Setup VERSION.exe"
Make your changes to Firefox in the core subdirectory.
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.
Run this command:
copy /B 7zSD.sfx+app.tag+app.7z our_new_installer.exe
to concatenate the files and create the installer.
The “/B” is very important! It tells copy that these are binary files so it doesn’t add extra characters to the files.