Sometime ago, I reported this issue into Mozilla's bug tracker, but it seems it was completely ignored. Now, on FF 67, on my work computer, Aero Glass in FF still works correctly but on my home computer the CSS property "moz-win-glass" is ignored.
Maybe if more users report this issue to Mozilla, some developer will care about it.
https://bugzilla.mozilla.org/show_bug.cgi?id=1418759