I think you are probably screwed. Never use a stock ipsw with a jailbroken or unlocked iphone because it also updates the baseband or modem firmware to versions and those newer versions don't have the holes that the earlier ones had that allow the firmware to be exploited.

Anyway, you can check the usual iphone hobbyist sites to see if your phone with whatever firmware is now on it can be jailbroken and unlocked. The dev team/pwnage tool stuff is what I used to use, and I had to wait after every new firmware release for them to update their tools to support the new firmware release. Using their tools preserved the old exploitable baseband firmware on my phone, while updating the rest of it to the current version of the ios firmware.

-David