Below is a guide courtesy of Shaitan (via psx-scene.com/forums/content/tutorial-1888/) on swapping PS3 CFW, MFW and OFW Firmware without a USB device to install the PlayStation 3 Firmware you prefer.
To quote: I'm always looking for ways to make my PS3 experience easier so this was awesome. It's nothing special but I'm constantly needing to change firmwares like many of you so I thought I'd share it.
To do this it's best to use QA Flag Extra since most firmwares can not enable "System Update Debug".
1. Enable QA Flag Extra and go to the debug settings and enable "System Update Debug"
2. Use Multiman's file manager (or other) and create a folder in /dev_hdd0 called "updater", so it's /dev_hdd0/updater/
3. Create folders in that directory for the firmwares called 01, 02, 03, ect. (Don't miss a number or it will error).
4. Copy whichever PS3UPDAT.PUP into one of those folders and........
5. Rename it to whatever you want, you dont even need the .PUP at the end.
6. Go to System Update then Update via Hard Disk and it should look something like this:
P.S. Updates take only 3 minutes with this!