diff -up firefox-74.0/widget/gtk/nsWindow.cpp.1615098 firefox-74.0/widget/gtk/nsWindow.cpp
--- firefox-74.0/widget/gtk/nsWindow.cpp.1615098	2020-03-13 09:34:03.623433935 +0100
+++ firefox-74.0/widget/gtk/nsWindow.cpp	2020-03-13 09:38:44.382941288 +0100
@@ -4879,8 +4879,6 @@ void nsWindow::UpdateTopLevelOpaqueRegio
   if (window) {
     gdk_window_invalidate_rect(window, &rect, false);
   }
-
-  moz_container_update_opaque_region(mContainer, aSubtractCorners);
 }
 #endif