> continue being 7 MB, should not it diminish the size?

No.

Files cannot be made smaller, only larger.

To make the datafile smaller, you have to create a backup
and restore it, so that a new file is created.

But, Firebird will re-use the empty space inside the file
to store new records, so there's no real need to make
the file smaller again.

Martijn Tonies
Database Workbench - tool for InterBase, Firebird, MySQL, Oracle & MS SQL
Server
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