Check your "services option" in /etc/sysconfig/SuSefirewall2. FTP ports must be declared in the "EXT" services.

The ports 20 and 21 are declared in the "EXT" services.

Actually it is the other way round. You machine should have its high ports open and the server should have ports 20 and 21 open.

I don´t get that. I thought passive FTP is used so that I don´t have to keep these higher ports open if I only want to download stuff. If not, what´s the point ?