I searched the forums high and low and didn’t seem to find anything, so I figured I would post my findings and hopefully save someone else the headache.
If you are having problems updating the firmware on your SSD in your macbook and you have removed your superdrive (à la Optibay) and are trying to boot the ISO/disc from an external CD drive enclosure, it simply will not work. The update is linux based and will not recognize externals. You will need to either remove your SSD and put it into a computer that has an optical drive hard lined into the computer, or you will need to remove your optibay and reinstall your superdrive (just for the update). It’s a huge pain in the ass, I know… but the update will work fine afterwards. After you’re done the update you can remove your superdrive again.
Hope this helps!