if you intend to put the firewall outside interface into a VLAN and the ISP connection to the 3750 into another VLAN, then yes, two HSRP groups would be required.
you'll only need one HSRP group for every VLAN that you want to setup redundant routing for.
if you decide to keep the firewall outside interface in the same VLAN as the ISP connection, then one HSRP group will be required.
not exactly sure of your config or topology so if you want to share, we can better help you.