(c) Dmitry Kuzmenko, IBSurgeon, 21.05.2017
InterBase was created in 1985: it was the first commercial multi-versioning database. In the end of 1999 Borland decided to close InterBase development, and published its source codes under InterBase Public License. This code was copied (it is permitted by the license), and Firebird was born – from the version 1.0 Firebird is production-ready database, based on previous decades of InterBase development.
At the end of 2000 Borland turned back to closed source and commercial licenses (exactly as it was earlier) with InterBase, and started development of 6.5.
Firebird 1.0 was released in 2002, with many bugfixes and extentions of DDL and DML. The active Firebird development continued after 1.0, and in the 2004 the second major version of Firebird was released. Borland at that time also has introduced new versions (7.0 and 7.1). Firebird 1.5 and InterBase 7.0 was incompatible both by database format (ODS) and core functionality.
Since then, the difference between Firebird and InterBase became bigger. The migration from InterBase to Firebird and back with backup/restore is impossible since Firebird 2.0 and InterBase 7.0.
The only way for migration between current versions of InterBase and Firebird is through SQL script (with manual fixing of differences) and then pumping of data from the old database to new one. In our practice we did several such migrations for various versions of InterBase and Firebird – see more details here https://ib-aid.com/en/firebird-database-migration/
Below you can find the table with the list of differences between the latest versions: Firebird 3.0 and InterBase XE7