Firebird 3.0 package is uploaded and accepted in #Debian experimental
Firebird 3.0 is now uploaded and accepted into official Debian experimental repository (this is the first upload so things will break also you must backup database from 2.5 and restore into 3.0)
You can read install guide for firebird 3.0 on howto access the experimental repository.
Please report any problems you may encounter. The packages should be installable right away (and automaticly remove any existing firebird2.x ones)