Well, I use KDE/Mozilla and have one theme installed... "SkyPilot" and here is where it put the .jar file: (remember, /.mozilla is a hidden file)
~/.mozilla/default/8vgn05n0.slt/chrome
It did install itself when downloaded from the them site at
http://themes.mozilla.org
so I don't know if the /chrome folder is for all themes or just that one but you can check the default folder on your install.
KC