diff -up firefox-65.0/widget/gtk/nsWindow.cpp.1196777 firefox-65.0/widget/gtk/nsWindow.cpp
--- firefox-65.0/widget/gtk/nsWindow.cpp.1196777	2019-01-28 14:37:27.470163867 +0100
+++ firefox-65.0/widget/gtk/nsWindow.cpp	2019-01-28 14:41:52.479064393 +0100
@@ -156,7 +156,8 @@ const gint kEvents =
 #if GTK_CHECK_VERSION(3, 4, 0)
     GDK_SMOOTH_SCROLL_MASK | GDK_TOUCH_MASK |
 #endif
-    GDK_SCROLL_MASK | GDK_POINTER_MOTION_MASK | GDK_PROPERTY_CHANGE_MASK;
+    GDK_SCROLL_MASK | GDK_POINTER_MOTION_MASK | GDK_PROPERTY_CHANGE_MASK |
+    GDK_FOCUS_CHANGE_MASK;
 
 /* utility functions */
 static bool is_mouse_in_window(GdkWindow *aWindow, gdouble aMouseX,