If you're connecting yourself to the ethernet0 port on the firewall, I'm assuming your using a crossover cable. If you plug into the switch you're using a straight through cable. The speed problem may be coming from a mismatched speed/duplex issue with your computer negotiating with the switch. If you have a managed switch, set your port speed to 100/full on the switch and on your workstation and see if you have any problems then. If you still have issues, do the same between Ethernet0 on the firewall and the switch. This should resolve your problem.
