It is only one year old, released May 9, 2018
Seems a lot of my add-ons are also disabled,but the one that concerns me is the Classic Theme Restore. So long as I leave that for now, even disabled, the look I spent time to make FF look the way I wanted, remains. I just noticed my "night light" addon is gone too. I'm with others, finagle with security needs, but leave the add-ons alone.
April my Linux mint 17.3 support ended, so probably upgrade to version 19.2 and do the FF upgrade at the same time in a couple months. I think I can walk into 18, then into 19 without doing it all again from scratch, but not sure since init was replaced by systemd in version 19.