Shared config woes (autoadmin.global_config_url, general.config.filename etc. on Linux)

I'm trying to set up global defaults (shared preferences) for Mozilla 
1.2.1 on Linux (yeah, I know there are newer releases, but this is the 
one distributed with the OS.) I've tried several different ways, but 
none has worked 100% so far. Problems:

1. pref(autoadmin.global_config_url, ...) appears to have no effect.

2. pref("general.config.filename", ...) does have an effect, but I'm not 
able to get Mozilla to actually read the given file; I'll just get a 
popup that says the load failed, without explaining why.

3. Simply adding pref() calls to the .js files (all.js, unix.js or 
whatever) mostly works, but I can't set all the prefs I wan't that way. 
In particular, I'd like to set up e-mail account details based on the 
current user login (I can see no reason why every user should need to 
set up this, since everyone will be using exactly the same settings, 
except for the user name and sender address, which can be extracted 
directly from the login environment.) Essentially, I want to put the 
output of getenv("USER") into some of the pref settings, but the 
getenv() function isn't available at this stage.

Help, anyone? Does global_config_url work at all? Is there any way I can 
find out exactly why config file load (method 2)) fails? Also, is there 
any way at all I can extract information on the current user from within 
the .js files? Actually, I'd prefer method 3) in many ways as it saves 
me from enconding the data (and installing special utils to do it.)

- Toralf