HI, Marlon, sorry for the delay. I don’t come here daily.
I think that you are hitting the big button that read creat IPSW with the left button you have to use the right click button on the mac. after you hit Create IPSW with right click a menu will appear with may firmwares, select 4.3 (8F455) and it will download it for you.
if no right mouse button is present in your mac you can use the Control Button on the Keyboard. Just press the control button live it press and then left click the menu will appear select your firmware and it will download it for you.
I will check tomorrow to see if you manage to Jailbreak it.
Also try downloading the Firmware manually from any trusted site, I use iClarified, and after you download the IPSW you put in in a folder called Tether that is inside the Documents folder of the Mac.