Since you cannot use BlackBerry World, you must "sideload" the app using a .cod or .jad file. This involves transferring the installation file from a PC to your BlackBerry 9900 via USB or Bluetooth.
BlackBerry asked: "Allow application permissions?" download facebook app for blackberry 9900
BlackBerry 10 and BlackBerry OS Services FAQ — End of Life Since you cannot use BlackBerry World, you must