You can use Data Synchronisation Studio with Firebird via the ODBC connection provider and the Firebird ODBC Driver.

Ensure you have the Firebird/InterBase ODBC Driver installed and if you have Data Sync 64 bit edition you also have the 64 bit version of the ODBC Driver.

Select the ODBC Driver and enter the connection string to Firebird like this.

DRIVER=Firebird/InterBase(r) driver;UID=SYSDBA;PWD=masterkey;DBNAME=C:\Temp\EMPLOYEE.FDB

Then select the Object in the database or switch to the SQL Tab and enter your own SQL.

Once the Schema Loads you can start defining your Project.

Or just preview the Data to check the connection.