I use QuickDesk, that is commercial:
http://ems-hitech.com/quickdesk/.
Another good product seems to be IBWorkbench, with a special, less priced edition, for Firebird only:
http://www.upscene.com/
If you want a free solution, for Windows and Linux, have a look at IBAdmin:
http://sourceforge.net/projects/ibaccess
regards
Marco Menardi