OPNsense

ZFS-Snapshots

Create a new Snapshot with the name known-good
Upgrade Firmware
Reboot and test
OPNsense works as expected:
- Remove the known-good Snapshot and keep using the default Snapshot
OPNsense has issues:
- Activate the known-good Snapshot either in the WebGUI or the Boot Menu
After rebooting, remove the bad default Snapshot
- Rename the known-good Snapshot back to default