I would think the about:config entries discussed are ex-factory set to values each user has to change individually, after the installation has run its course. The solution could be to have patched files ready to install post factum:

A Brief Guide to Mozilla Preferences - MDN

Firefox will check for a couple of different external files at startup. These are mentioned in the above-linked article, but here are some other resources:

• user.js (in the user's Firefox profile folder) - info: http://kb.mozillazine.org/User.js_file
• mozilla.cfg (in the program folder) - info: http://kb.mozillazine.org/Locking_preferences

Since these can override the default settings, one or the other might be useful for pushing out settings.

If you are thinking about group policy or other centralized solutions, you could consider joining the enterprise mailing list where you are likely to find more expertise on implementation than here in the forums. See: http://www.mozilla.org/en-US/firefox/organizations/.

You can use a mozilla.cfg file in the Firefox program folder to lock prefs or specify new (default) values.

Place a file local-settings.js in the defaults\pref folder where you also find the file channel-prefs.js to specify using mozilla.cfg.

pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0); // use this to disable the byte-shift

See:

• http://kb.mozillazine.org/Locking_preferences

These functions can be used in the mozilla.cfg file:

defaultPref();  // set new default value
pref();         // set pref, but allow changes in current session
lockPref();     // lock pref, disallow changes