After 5 hours of fairly heavy CPU load with no progress, I cancelled the firmware update, rebooted and tried again. This time the progress bar came up and it only took a couple of minutes for the update to complete.
Lesson learned: If the firmware update takes more than a few minutes and the updater doesn’t give you any feedback, it might be caught in some kind of loop. Exit and try again.
My WD MyBook Essentials 2TB drive is now at firware 2.018, WD SmartWare software version 1.3.2.5.
Reference page: http://www.wdc.com/wdproducts/wdsmartwareupdate/Step1.asp?id=wdfMB_Essential&os=mac
