I just tried setting a default already present in the /etc/firefox/pref/firefox.js file from 'false' to 'true' - and it has no effect on the configuration when restarting FF3 and peeking at the value in about:config.
It looks to me like the /etc/firefox/pref/firefox.js is completely disregarded by Ubuntu (I'm using 8.04.1).
I just tried setting a default already present in the /etc/firefox/ pref/firefox. js file from 'false' to 'true' - and it has no effect on the configuration when restarting FF3 and peeking at the value in about:config.
It looks to me like the /etc/firefox/ pref/firefox. js is completely disregarded by Ubuntu (I'm using 8.04.1).