Firebird 0.6 shows the same issue there was with Mozilla on my system (W2K): It locks the taskbar when it starts, so clicking on the minimized windows in the taskbar doesn´t work and I only can access other applications via alt+tab. There is a second (minimized) window opened by Firebird/Mozilla, called "Netscape Dispatch Window", that shouldn´t be there AFAIK.
This is really annoying and it kept me from using Mozilla. But I have no idea what´s going on
BP6, RU BIOS, XP SP3, ACPI, 2x366@523(1,95V), Pentalpha HS + 1x 12cm fan @5V, 768MB, Powercolor Geforce 3, RTL8139D NIC, Terratec EWS64L, Samsung M40 80GB (2,5''), LiteOn CDRW