Comment # 7 on bug 1053959 from Wolfgang Rosenauer

I'm just more and more confused ;-)
Probably I also don't get how to reproduce it.
What is an "inactive" window? If it's fully inactive how would you scroll at
all in it? Probably I have in theory the same issue but never noticed.

Just to be sure. FF 52.3 from TW works correctly? What about 52.3 from 42.x?
Just wondering because the latter is built with Gtk2 while all the others (52.x
on TW and FF > 52 are all built with Gtk3).

Good finding of the MOZ_USE_XINPUT2. Please report your findings when playing
with that.