No simple answer unless you live in hacking/ encryption/ land. If your ps3 model is less than the 3000 series, you can downgrade with a hardware flasher to a cfw regardless of the fw you are currently on I believe.
3k and 4k models are unhackable/undowngradable unless the near impossible happens, and some sort of master key is leaked, as it is doubtful $0ny made additional encryption mistakes to allow hackers to get them now.
This post names some keys, but much more is needed to truly understand the significance. http://www.ps3news.com/forums/ps3-cf...-125749-3.html