When you try to drop database with i.e. running transaction, you get:
drop database;
Statement failed, SQLCODE = -901
lock time-out on wait transaction
-object /fbsql/marisa.fdb is in use

but I'm using only aliases and access is setted to None (DatabaseAccess param) in firebird.conf.

The show database command shows only the alias:
show database;
Owner: TESTIK
Default character set: NONE
Database: marisa
    Site: cincura, cincura, x2acer
Version: LI-V6.3.0.12748 Firebird 2.0

Creation date = 2007-01-22 21:19:59.0330
Page size = 8192
Number of DB pages allocated = 31818
DB buffer pages = 0
Actual buffer pages = 2048
Database SQL dialect= 3
Sweep interval = 20000
Forced Writes are OFF
Read Only flag is OFF
Reserve flag is ON
Transaction - oldest = 232
Transaction - oldest active = 233
Transaction - oldest snapshot = 233
Transaction - Next = 233
ODS = 11.0