https://bugs.freedesktop.org/show_bug.cgi?id=65377
--- Comment #4 from Henri Verbeet hverbeet@gmail.com --- I think it depends a bit on the specific model, but many Macs will only boot EFI from USB. Refind (http://www.rodsbooks.com/refind/index.html) is potentially a way around that, although I'm not entirely sure if that counts as booting in EFI mode or in BIOS mode.