Refer to Downgradable/Hackable PS3 Models and see downgradable min praxis.
Your PS3's base firmware (The original starting firmware that it first had) must be 3.55 or lower.
I do not recommend attempting to downgrade a PS3 yourself.
Only FATs and early SLIMs can downgrade.
EBOOT RESIGNER 4.46 YOUTUBE UPDATE
Alternative method: MinVerChk (Min Version Check) This is a fake update that autofails and gives you your lowest base firmware.
Refer to the Downgradable/Hackable PS3 Mdoels at the very bottom for model numbers.
You can, however, downgrade the firmware.
You can't jailbreak directly off firmwares higher than 3.55.
My PS3 is "insert OFW here," can I jailbreak it?
Format the 2nd Empty One every CFW Installation/Update.
One for normal storage, homebrews, and backups and a second empty one for future CFW installations and/or transferring very large files.
I recommend SanDisk since it's the easiest one to purchase and get a nice 4GB or even larger if you plan to put a few game backups on it.
You will always be using this for changing firmware, installing and running homebrew, and using it as an external backup storage device. There is no workaround for it since Sony patched the exploit in 3.56. It is modified firmware to allow the PS3 to perform tasks it was not meant to perform such as playing backup games, for example.
OFW stands for Official Firmware and, as the name implies, it is Sony's official firmware that they developed to run their system.