Its possible in this way:
2. installation and customisation
3. close FF
4. make this folder in program directory: distribution
5. make this subfolder in distribution: extensions
6. place the extension in this folder BUT be aware it doesn't work with the standard file. You have to install it in a similar FF browser version and then copy it from the profile folder. This results in a renamed version which is needed.
7. Don't start FF make a Postscan instead.
8. Build and be happy :-)
This was not my investigation. I got help from the great VMWare Support!