[Darryl Ramm]

Avid official support and updates for these drivers ended long ago. If it works at all on a recent macOS are lucky. Product end of life was back in 2016. You should be searching around if stuff is know to work before you upgrade the OS and/or it may be time to start looking for new interfaces. None of this is related to the interface being Firewire.

I posted because I thought I had a link for you, turned out it was Mbox 3, so no help.

I would not be surprised if it did not work.

You can look in the macOS System Report and see if the Firewire device is listed, is it there with a name or no name etc.
You can try use "kextstat -l | grep digidesign" to see if the driver is loading.
You can try reinstalling the device driver. And look for any security warnings.

No luck, then roll back to your backup. You did make a backup right?

If you get it recognized as a device you also have to enable is as a "mic input" in Mojave security settings for any audio inputs to work. (you can search for more details on that).