You can pre-configure Mozilla so that all users get the same preferences when they create a new profile. For example, you might want to define a preference for /tmp, or /Users/Shared as the cache directory, so that users with network home directories will use the local drive for cache. These prefs are stored in a javascript file called user.js which needs to be saved to /Applications -> Mozilla.app (control-click and select "Show Package Contents") -> Contents -> MacOS -> defaults -> profile -> US -> user.js. In your user.js file, lines which begin // are comments, so you could enter, for example:
//
// user.js: Personal prefs which mozilla shouldn't overwrite.
//
user_pref("browser.startup.homepage", "http://www.my.server.edu/");
user_pref("intl.accept_languages", "en-au, en, en-us, zh, zh-cn, zh-hk, zh-sg, zh-tw, fr, de, de-de, de-at, it, ja, pl, ru, es, sv, fi, sr, hr, da, nl, fr-ca, fr-fr, id, in");
user_pref("intl.charset.default", "UTF-7");
Note that user.js has unix line endings, so use a command line text editor, like vi or pico for editing ... or use BBEdit with the appropriate setting.
For the sake of completeness, I've got the same file at /Applications -> Mozilla.app -> Contents -> MacOS -> defaults -> profile -> user.js, which is where it should be, except that the version I downloaded from mozilla.org turned out to be a US build.
Whenever a new profile is created, a copy of user.js is automatically written to ~/Library -> Mozilla -> Profiles -> profile_name -> randomString.slt -> user.js. When Mozilla runs, it reads its preferences first from that profile, and lastly from the application directory:
- ~/Library -> Mozilla -> Profiles -> profile_Name -> randomString.slt -> prefs.js -- stored from last session
- ~/Library -> Mozilla -> Profiles -> profile_Name -> randomString.slt -> user.js -- persistent prefs
- /Applications -> Mozilla.app -> Contents -> MacOS -> defaults -> pref -> all.js -- persistent admin prefs
I set up Mozilla so the preferences were as I wanted, then quit. Next I copied the lines I wanted from prefs.js to my own user.js file. Then I saved user.js to /Applications -> Mozilla.app -> Contents -> MacOS -> defaults -> profile -> US -> user.js, so that everyone would get these prefs whenever they created a new profile.
You can read more documentation in mozilla.org's A Brief Guide to Mozilla+Netscape Preferences.

