I want to use the Query-Execution-Plan from DBeaver for a Firebird 2.5.1, but there are always no details or costs listed. Is there something needed in the connection driver properties or somewhere else?
Like user13964273 commented, this is available in Firebird 3 and above:
Firebird cannot show cost in plans. Detailed plan is available starting from version 3 so 2.5 cannot provide it anyway.