Apologies for the required work-around to GitHub being silly.
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Click the link to the firmware.
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Click the "Raw" button.
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Right-click the page and "Save As..."
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In the "Save As..." dialog, remove the ".txt" extension so the file is saved with a ".hex" or "*.bin" extension.
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Install using your favorite flashing tool, such as QMK Toolbox, dfu-programmer, Atmel Flip, etc. Note that in many cases, you can hold down the top left key of your keyboard when inserting USB plug to put the PCB into "bootloader mode".
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After flashing new firmware, restart the firmware application inside the flashing tool, or just unplug and plug USB.
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VIA should detect your keyboard and display the default layout.