Code:
This is what I did
Placed custom firmware in C:\
Start>cmd>rightclick run as admin
Type" cd..
Type: cd.. again
now type: irecovery.exe -p C:\iPhone3,1_4,1_8B117_Custom_Restore
follow instructions (launch GP, place iphone in DFU mode, click jailbreak)
Once it says Jailbreak done
Go back to the CMD window and press Enter
(screen should turn white, red or blue)
Now open itunes CTRL+RESTORE and select custom ipsw from C:\