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.

Step One:

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 ESR from here and of rapid release from here.

Step Two:

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 Three:

Make your changes to Firefox in the core subdirectory.

Step Four:

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 Five:

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

Step Six:

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.