How to upgrade the firmware at MAC OS?

First, upload dialog in Chrome (select a file from your computer),

Click Other to select All Files, otherwise, the .pkg files will be greyed out and cannot be selected.

In Chrome’s dialog go to > System > Firmware Upload (select a file from your computer),

Click “Options” – then click the format popup, (show) all files. Otherwise, the .pkg file may be grayed out and cannot be “committed”.