Peter's instructions are accurate. Firmware is operating system agnostic. The file for the camera is the same regardless of the OS you select (windows or MAC).
5D300136.FIR is the file you need.
~Rick
Bay Area - CA
~R5 C (1.0.9.1), ~R50v (1.1.1) ~RF Trinity, ~RF 100 Macro, ~RF 100~400, ~RF 100~500, ~RF 200-800 +RF 1.4x TC, BG-R10, 430EX III-RT ~DxO PhotoLab Elite ~DaVinci Resolve Studio ~ImageClass MF644Cdw/MF656Cdw ~Pixel 8 ~CarePaks Are Worth It
