Enable and document support for AutoConfig/MCD

Binary package hint: firefox-3.0

Mozilla Firefox provides a mechanism allowing centralized auto-configuration known as AutoConfig, or "Mission Control Desktop." Some references:

    https://developer.mozilla.org/en/MCD,_Mission_Control_Desktop_AKA_AutoConfig
    http://mit.edu/~firefox/www/maintainers/config.html

This is a useful feature to have in large installations of Ubuntu. It has at least two advantages over modifying /etc/firefox-3.0/prefs/firefox.js:

1. Configuration code can be fetched from a remote server when the browser is started;

2. The Javascript code can do a bit more than what is allowed in a prefs file, e.g. access environment variables with getenv() and use them in pref values.

The Ubuntu (Intrepid) firefox-3.0 package, however, does not appear amenable to the use of this mechanism. There is a firefox.cfg file in /usr/share/doc/firefox-3.0/, but nothing in this file indicates how it should be used. There is no .../greprefs/all.js file in the package, and as that is where the Mozilla and MIT docs indicate that one should add the "general.config.filename" pref, it's not clear where that should go. It's not even clear that the browser was built with the "pref" compile-time extension enabled in the first place.

I would like to see some sort of explicit AutoConfig support in firefox-3.0, ideally a situation where a typical institution need only modify files under /etc/firefox-3.0/ to get that up and running.