Comment # 8 on bug 1053959 from Jiri Slaby

In KDE/plasma, open one firefox and one other window (e.g. xterm). Switch to
xterm by alt-tab making firefox an "inactive window" = in background. Even
though firefox is inactive, you still can scroll the content by using mouse
scroll wheel over the inactive window (while xterm is still in foreground =
active). That does not work with MOZ_USE_XINPUT2=1.

Works:
versions up to 52.3

Does not work:
version starting 54

No matter which repository I use (42.3 repo on TW installation, TW repo on 42.3
or on 42.2).

So only the ff version matters, exactly the one which added MOZ_USE_XINPUT2=1.

Needless to say that I use no touchpad, it's all with mouse.