Problem: "show conn flow-rule qos" [followed by any input] gives "Syntax Error: Illegal parameter"
Fix: first enter "system support diagnostic-cli" and then "enable", THEN you can run e.g. "show conn flow-rule qos 268444269"
I first found the qos rule-id because I knew the IP I was looking for:
> show conn address 10.1.2.3 detail | include uptime
flags xaA N, qos-rule-id 268444269, idle 12s, uptime 21s, timeout 30s, bytes 0, xlate id 0xffcbe37c00
flags xaA N, qos-rule-id 268444269, idle 1s, uptime 1s, timeout 30s, bytes 0, xlate id 0xffa7ba0b80
flags xaA N, qos-rule-id 268444269, idle 12s, uptime 21s, timeout 30s, bytes 0, xlate id 0xffa46bc680
FTD 7.2.9 (and probably all others) affected.
TAC reports an enhancement is open but not prioritized.