Talking about Linux?
Sure you can, but you have to chown the configuration files, so that they will be accessible and writable by the user in mind, and ONLY by him.
For example, copying the whole (hidden) .mozilla folder from the user account to the root account (overwriting everything there) and then chowning the whole copied folder and contents to "root/root" should suffice.
But then practically it has little point: The root account should NOT be run with GUI- much preferrable is using a root console, or if you explicitly need running application "foo" as root, doing it as "kdesu foo" (if you happen to use KDE), or "gksu foo" (if you happen to use Gnome).