If FreeNAS 8 encounters an error (which is usually related to out-of-memory conditions) it will enter debugging mode, which is indicated by the following debugger prompt:
db>
To disable this, and enable automatic reboot on panic, add the following tunable in System > Tunables > Add Tunable:
Variable: debug.debugger_on_panic
Value: 0
Make sure enabled is checked and hit Ok.
Questions and comments are welcome in the comments section below. Thank you!