okay now what you will have to do is boot your PS3 into what called recovery mode to do this you..
1. Make sure your PS3 is turned off.
2. hold the power button until it turns on and then shuts down again.
3. Then hold the power button again until you hear a beep followed by another 2 beeps.
4. release the power button. You will boot into the recovery menu.
Once done this it should recognise your usb. as for the firmware download the OFW (Official FirmWare) off the Playstation website.
Then once all that is done install your desired jailbreak.
I hope this has helped if so + Rep