I have installed (Kicad deleted and …/Roaming/kicad deleted) 5.1.0 Windows 7 64 bit.
Do you see footprint list in footprint editor like me - each element twice?
Double clicking at one in list selects two (the same) - see screenshot.
There are no two files for each footprint on disc.
During first opening Footprint Editor I got few errors. But next opening no errors.
Because of these I’m not sure - should I reinstall KiCad or report a bug - so: Do you see each footprint twice, like me?