scp is an integral part of ssh so you can use it with no additional package required on IPFire. You need to ensure that you have ssh on your desktop machine.
You access scp from the command line in a terminal on your desktop machine as follows:-
scp -P 222 root@your-IPFire-host-name:/source-directory-path-on-IPFire/filename-or-wildcard /destination-directory-path-on-desktop/
This will copy from your IPFire to your desktop. If you want to do it the other way around the order is the source directory/filename first then the destination. The -P 222 is to specify the port, as IPFire uses 222 instead of the default 22.
Hope this helps.