Firebird didn't exist in the 1990s, so if it is from that time period,
it is unlikely to be a Firebird database. It could be an InterBase
database, but then I'd still have expected gstat/Firebird to produce a
non-zero ODS (and then, having an extension FDB doesn't make much sense).
Looking at the first few bytes of the file, it is not a Firebird or
InterBase database.
Given it seems to reference images (and based on
https://fileinfo.com/extension/fdb), it could be "Extensis Portfolio",
an image organization program, which has, in one form or another,
existed since the early '90s.
Mark
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Mark Rotteveel