This firmware was released 11 Dec 2017 but could not be installed if your computer was a Mac running OS Sierra 10.13. They have since worked around this Apple generated issue. The firmware update is very complex involving two downloads and performing steps in a very specific order. But it works.
Here is a link to the Sony Firmware update page for Mac:
https://esupport.sony.com/US/p/swu-download.pl?mdl=ILCE7RM3&upd_id=11366&os_group_id=3