The FW packets with FW older than 2.0 contain so called Firmware Update (UpdateFirmware) tool that was used to upgrade the sensor with an older versions of the FW:
There is no need to use the UpdateFirmware tool to flash any FW on the sensor any more. All the FW releases, custom or general, can be flashed using the zForceProgrammer.
However, the zForceProgrammer requires dfu/hex file to be pointed in the explorer. Once you push Open FW file button you are asked to pinpoint the dfu/hex file:
You need to unpack the .nfp file provided in the FW packet (prior to FW version 2.0):
In the unpacked folder you will find all dfu/hex files for the FW.
Pinpoint the required file in the zForceProgrammer and push Write Firmware button.