Comment # 6 on bug 1053959 from Jiri Slaby

$ osc rdiff mozilla firefox52 mozilla firefox54
shows:
--- mozilla.sh.in (revision 16)
+++ mozilla.sh.in (revision 5)
@@ -102,6 +102,9 @@
 # disable Gnome crash dialog (doesn't make sense anyway)
 export GNOME_DISABLE_CRASH_DIALOG=1

+# enable xinput2 (boo#1032003)
+export MOZ_USE_XINPUT2=1
+
 moz_debug=0
 script_args=""
 pass_arg_count=0


And indeed this fixes it!
# enable xinput2 (boo#1032003)
#export MOZ_USE_XINPUT2=1