Before attempting a downgrade, you need to know the "Base Firmware" your console shipped with. If your base firmware is 4.89 or 4.90, you cannot go back to 4.88. Download the tool.
If your goal was to get back to a "clean" 4.88 Official Firmware (OFW): Install the 4.88 CFW first using the steps above. Once on CFW, the system restrictions are gone. how to downgrade ps3 firmware 4.89 to 4.88
💡 If your console is a Super Slim and you just want to play backups, skip the downgrade. Simply install PS3HEN 4.89 , which provides similar features without the risk of bricking your hardware. Before attempting a downgrade, you need to know
Plug the USB into your PS3 and attempt a System Update via Storage Media. If your goal was to get back to a "clean" 4
Always verify the MD5 hash of your firmware files to ensure they aren't corrupted before installing.
If the power cuts during the Flash Memory Patching (Step 2), your PS3 will become a "brick" (unfixable).