Advantages:

• Firebird database is a lightweight and easy to install.Only an executable or a script according autoninstalable platform.
• It consumes huge resources on the server.
• It's fast and powerful. (See Limits Firebird).
• It has a similar type of license to MPL (Mozilla Public License), which
  allows for free use and distribution with a little restrictive.
  Example:
  Allows its use in our applications without the obligation of having to
  publish the source code of the same.
• You can use external libraries that improve the operation of Firebird.
• There is an ODBC driver for Firebird.
  ODBC Firebird
• There are many components for various programming languages for
  Firebird connect natively or indirectly.