How to downgrade your PS3
I've been looking up about a lot of homebrew stuff for the ps3 (the nes emu stopped working with the 2.50 FW)
But it seems it is super ez to downgrade.
Just look here.
1. Download the wanted firmware
2. Rename it from XXX.PUP to PS3UPDAT.PUP
3. Copy the file on any external device, such as an MS, on the ms0:/PS3/UPDATE folder
4. Run it under the PS3. Done.