Alex, this is wierd. The switch configurations you sent, should not cause any problem with your topology. So look for any loops, ip conflict, watch the switchs for broadcast storms etc.
I think you should try step by step to find the root cause. Just connect one switch to firewall, then connect a PC to the switch. If it works, connect another PC to the same switch. Then go on step by step. Only connect one device at a time, then check if it still works.
Regards,
Rahman