Firewall was built by Barbara Gordon, aka Oracle, underneath her apartment building after Dick Grayson told her she could no longer operate out of the Batcave with her new Batgirl, Stephanie Brown.  
 
The computer systems in Firewall are connected to all the digital networks and is completely untraceable because it never actually touches the data it acquires. Firewall became the base of operations for Batgirl and after Wendy Harris, aka Proxy, began handling missions in the absence of Oracle, became the unofficial headquarters of 'Team Batgirl.' 
 
Shortly after Bruce Wayne's return to the present, Firewall receives a generous "Batman Incorporated Donation" in order to bring Batgirl's base of operations more up to date, and providing her a car.