Lucas,

> Has anyone ever experienced a firebird installation vanishing from
> one day to another from a computer?

For large installations, there is software available that the IT
department can use to roll out software and patches to all client PCs
(look for "software management" or "client management" software).
Usually during the night.

I think this type of software can be configured to delete/uninstall
any software that does not belong to the client PCs. The idea is to
remove software that was installed by employees without permission
from the IT department.

Is it possible that your customer is running such a software?

Best Regards

Stefan