Providers have policies (for several good reasons) about how endpoints are managed and most of them (especially the big ones like Cox) require that in order to connect to their network, your cable modem must run their firmware. I was under the impression during initial connection handshake the cable modem downloads the appropriate firmware (every time, no matter what) and installs and runs it. Trying to update the firmware to some other version would only result in losing connectivity until you reboot the modem, at which time it will load again from the network.
Cox technical support should be able to identify the firmware version and verify it is the latest supported version for the Cox network.