This may work for you because you already had the theme installed but I believe if you uninstall it and then try to install it again to FF 18.104.22.168 it might not take. When I drag and drop the nuovext zip file to the add-ons area of FF it installs but the restart button is grayed out and the installation does not apply.
Perhaps I'm installing this incorrectly but usually if the theme is saved as a zip or rar file, simply dragging and dropping it to the add-ons area of FF automatically installs it without any problems unless the theme needs to be updated.
If there is another way to install this please let me know. Your theme is beautiful and I would like to use it.