Has it been that long ago? Yes, yesterday, Firebird celebrated its 10th anniversary as an open source project.
It was stable for almost 2 years, and then Firebird 1.0 was released more than 8 years go.
The next version, 1.5, also took less than 2 years, and was released more than 6 years ago.
Version 2.0 was a major release, and took a bit longer: 2 years ago.
Version 2.5 is taking the same speed as 1.5 did, and is about to be released.
Work has already begun on 3.0, and a lot of new features are in the pipeline, including a new ODS.
–jeroen