Quoted from DrMark12PA:
I'm trying to save a new copy of the firmware and the small "floppy disk" save icon doesn't seem to do anything
Spikes firmware are too big to be loaded into memory. As a result, each modification you make is immediately written to the file.
The "Save" button makes every modification you made "consistent" so that the game can accept the modified firmware. This is also automatically done when you quit Pinball Browser (provided you modified something in the firmware) : you generally don't need to use the "Save" button on Spike firmwares.
If you modify a Spike firmware and your computer crashes before you quit Pinball Browser or click on "Save", the modified firmware would be rejected by the game. In this case, just open the firmware and click on "Save" to make the firmware consistent again.