I've asked to Roman the following JIRA installation issue with
Firebird/Jaybird:

I've read that Firebird 2.0 solve index 252 length limitation of
Firebird 1.x. But when I'm installing Jira (Bug tracking software
http://www.atlassian.com/software/jira/) with Firebird 2.0 (last
release 2.0.0.12484), and using Jaybird 2.0 JDBC driver (last
release JayBird-2.0.1JDK_1.5.zip) i still have this index limitation
issue.
What is hapenning?

And Roman respond me:

So, to be sure that you solve your problem, please ensure that:
- you have created database with new ODS structure; this usually
means simply to ensure that you use isql from FB 2.0, fbclient.dll
is from FB 2.0 and fbserver.exe is from FB 2.0;
- your database page size is something bigger than 1k.

The tested solution:
The problem was that i have an older Firebird database structure,
ODS v10. But when i've recreated this from isql with ODS v11
structure, JIRA don't report me any errors.

Thanks Roman!
Mikel