(EP 10) How to Downgrade PS3 CFW by MrMario2011.
The general steps can be outlined as follows, but remember, these steps are generic, and you should consult specific guides for your model: how to downgrade ps3 firmware 4.89 to 4.88
Now that you have prepared your PS3 and gathered the necessary files, it's time to begin the downgrade process. Here are the steps to follow: (EP 10) How to Downgrade PS3 CFW by MrMario2011