How to downgrade from 3.56
You will need these files. http://www.multiupload.com/WTM75Z712C
UPDATE: I WILL RELEASE A VIDEO TOMORROW. I WILL RELEASE SOMETHING THAT AUTO BRICK YOUR PS3 TOMORROW ALSO.
I can confirm this works, but if someone else would confirm, that would also be nice.
This process is pretty simple..
First, you must force brick your PS3. Sounds like a stupid idea right? Well, you can UNBRICK your console, and I'll tell you how also. How does this work? Once your PS3 is bricked, you will upload the current files that I presented you with, and you will install them via the PS3, as your PS3 is bricked. I will show you how in 1 minute.
First off, you need to brick. There are several ways of doing this. This may take a few times, but you can be in the middle of installing a firmware, and shut your PS3 off, or you can install another Custom Firmware that has a chance of bricking your PS3. Installing a homebrew app that permanently writes to the NAND, causing a brick. No you may sound stupid if your going to brick your PS3 on purpose right? Well yes.. You are stupid if you do unless your going to downgrade.
Step 1.) Download the files I linked above.
Step 2.) Format a USB with NOTHING on it, and put the lv2Diag file from folder 1 on your USB, along with the Firmware you want to have on your PS3, such as a Custom Firmware.
Step 3.)Put your USB on the right most USB port on your PS3. (Closest to the Disc Reader.) Turn on your PS3, your screen will be black. Wait, your PS3 will turn off by itself. If it does not turn off within 25 minutes, manually turn it off.
Step 4.) Turn your PS3 back on, and you'll see the recovery menu. After this, erase everything else off of your USB, and put the 2nd lv2Diag file on the USB. (From folder 2)
Step 5.) Turn off the PS3, and put it on the right most USB port again. Then turn it on, it will then be unbricked with the firmware you chose.
Source : http://www.transamgrafx.net/index.php