If you have a DS708 with old software that works just fine, I would not risk doing some sort of available firmware update and then doing the final updates to the vehicle make software. The DS708 used to be the Flagship scanner that Autel claimed to be at 90-95% of the Factory tool capability and do could do almost everything except cut cheese, but after Maxi Sys came out it somehow got dismissed as almost an entry level , oil bay scan tool with Minimal coding capability. I believe the later updates after 2014 may have Dumbed functionality down due to lawsuits and possibly to make the newer faster platforms seem more attractive as it was being phased out. Do you trust the free update for DS708?
If you have a non functioning DS 708, by all means take advantage of your last chance to update to the final version software level and possibly get a brick working again, however if you have a perfectly working DS708 and just want to get an extra model year of coverage, and find out that the firmware update does something internally that prevents you from using your older software for old functionality, I wouldn't be surprised it even times out the tool.
Unfortunately Support is not to be found on here to answer your question about what the firmware does, so you just have to assume it's something court and not in your best interest, and give you a little bit newer car model coverage for some makes in exchange for disabling certain court contested functions.
Has anyone that has updated their old DS708 to current level (since the updates has been made free) , tried their old back up software SD cards and see if they can work on Ford ?