> - Firebird is file-based.

To make it clear:

On PostgreSQL an database consists of an directory containing many files.

On Firebird an database can consist of a single file (or several files
or an device).

On PostgreSQL there is an registry of all available Databases.

On Firebird the client has to know which File to use (besides
server-side aliases).

Another difference is the PostgreSQL usually cannot read databases from
previous Versions, you have to dump all databases before upgrading.

Elmar