A blanket or curtain of flexible fire retardant material is collapsed and retained within a retaining housing construction positioned adjacent to a curtain wall assembly for firestop sealing thereover. The housing includes a safing angle member secured to the curtain wall assembly and a cover which releases responsive to sensing fire conditions to allow the firestopping blanket to deploy downwardly to extend between curtain wall framing members and be positioned extending across a curtain wall panel for fire protection thereover. Such curtain wall panels are commonly made of glass which tends to fracture during a hot fire. The cover will release the blanket responsive to controlled failure of fusible links which secure the cover to the safing angle member. After deployment the blanket will deflect fire and heat away from the curtain wall panel to prevent the spread of fire to adjacent floors.