PS3 Homebrew Wiki
Master (v21.1b5)

Dual-boot Firmware

A dual boot firmware is a special firmware that takes an OFW and patches it so that you can install CFW over it. This is useful because it allows you to swap between OFW and CFW without downgrading or having a dual NAND/NOR, thus allowing you to log on to PSN more safely. You can find dual boot firmwares here. Dual boot firmware can only be installed on a console with CFW.