your information is correct.
ftp
server needs to have 2 port ranges open.
1st is control connection port (such as port 21, but can be any 1-65535)
2nd is data connection ports(any port range 1024-65535).
ftp
client can function without any open incoming ports by using PASV connections. however to have as little problems as possible it's better to open data connection ports on client as well, also in range 1024-65535. number of ports depends on how many ftp connections/transfers you usually have.
now if your firewall is showing that FlashFXP is using "1235,1424, 1436 4662" then you should throw it away becuase it's giving your wrong information. FlashFXP only uses consecutive port numbers.
if you want more detailed explanation of how ftp protocol works, read
http://slacksite.com/other/ftp.html