Advanced Installer is a program to create MSI files for Windows installer.
Advanced Installer is a generator for true MSI-files, not an imaging tool, not a setup-to-MSI converter (although it can optionally do that as well). Thus you can create true fully functional and reliable MSI-files.
The program comes with a simple to use graphical user interface. Once you have set up how to generate an MSI-file for a project, you can store that setup and run it again later (e.g. on a newer version of the program to be distributed).
It is ideally suited to create a firefox.msi file from an installed copy of Firefox. That's the reason why I mention this program here.
Advanced Installer can be downloaded from www.advancedinstaller.com. At the time of this writing both links "Freeware Edition" and "Free 30 day trial" lead to the same download page, because both downloads are identical.
The program function "Simple Installer" can continue to be used for free after the trial period. The whole program can be used for free for a trial period, but only for testing purposes. The program can declare Custom Actions, but this feature is unfortunately not available in "simple" projects. If you want to use advanced features like this, you must purchase a license. Price start at $299, it's definitely worth its price, and they have great support.