Comment 2 for bug 1169320

> After upgrading to Firefox 21 (beta) global preferences dir does not work now,
> package no more contain dir /usr/lib/firefox/defaults/preferences and link
> /usr/lib/firefox/defaults/preferences/syspref.js -> /etc/firefox/syspref.js

That's because the install layout has changed.

> I trying to use next dirs:
> /usr/lib/firefox/defaults/preferences - works on Firefox 20

That folder is for app preferences which are under browser/ and webapprt now

> /usr/lib/firefox/defaults/pref - does not work

Yes it does - we even use it for Ubuntu specific defaults. The problem with creating random files in either of these folders is that you need to understand the loading order of them. It's likely your custom setting is just overwritten by a file that's loaded afterwards

> /etc/firefox - does not work
> /etc/firefox/pref - does not work

We removed support for these from the packaging in Firefox 4.

> works only syspref config file /etc/firefox/syspref.js

This is the *only* supported way to customize system wide preferences on Ubuntu. As I mentioned above, if you're creating new config files in private directories outside of /etc then you need to understand the order in which preference files are loaded (both from the folders on disk, the omni.ja files and addons) and that it could change at any moment. You're pretty much on your own if you're modifying the Firefox install in this way.