IDK whether the problem is in the FF update itself or in the addon but after I update it to 66.0.5 FVD SD stopped working. It appeared as active in the addons list of the browser but opening new tab generated a blank new tab, as if the addon werent' installed. Reinstalling FVD didn't help, so I had to restore the whole system from an image containing FF 66.0.3 where FVD works fine.
I have blacklisted Firefox from updating for the moment but I thought you should know about this problem.
OS is Linux Mint 18.3.
Customer support service by UserEcho