Add the line
localDatastoreFormat=derby
to the global.properties file in the root directory of you configuration. Since 2015.02 firebird is the default local datastore format, if no format is defined.
Note that you have to delete the localdatastore when applying this change on the instance where you are changing the database, otherwise database files inside the localdatastore can corrupt your new localdatastore.
http://publicwiki.deltares.nl/display/FEWSDOC/global.properties+file
