Bricked UNO? Alternative firmwares?

The Uno doesn't have firmware. The ATmega328P has a bootloader.

  1. download the newest firmware (Arduino-usbserial-uno.hex - this was really tricky to find - or to download! Also using the firmware inside the Arduino software did not update the UNO),

That hex file is to program ATmega8u2 (or 16u2) used for USB to Serial communication. It has nothing to do with the ATmega328.