Default preferences

Hi,

In a local Firefox installation is it possible to set preferences at /Firefox/defaults/pref/all.js (or other name js file). It is useful for setting preferences to remain after every restart overwriting the user settings, or setting a mozilla.cfg file to lock some settings. We need it to lock some proxy settings before distribute the portable Firefox to our users.

I tried it with Firefox Portable and it doesn't seems to read Firefox/defaults/pref/*.js files. How can I do it with the Firefox Portable?

Thx