The new EV3 software tells me to update my firmware on the NXT. When I go to the tools menu and select update firmware it tells me the NXT brick can not support this function.
EV3 software will not download firmware to the NXT brick. For that you need the NXT-G software and a downloaded firmware file from Lego. 1.31 is the latest version.
So if you're running EV3 on NXT, you shouldn't throw out the NXT-G software. Once in a while, it's still needed.