diff -urN seamonkey-2.53.1-orig/mozilla/widget/gtk/nsLookAndFeel.cpp seamonkey-2.53.1/mozilla/widget/gtk/nsLookAndFeel.cpp
--- seamonkey-2.53.1-orig/mozilla/widget/gtk/nsLookAndFeel.cpp	2020-02-18 08:39:45 +0900
+++ seamonkey-2.53.1/mozilla/widget/gtk/nsLookAndFeel.cpp	2020-03-08 23:42:14 +0900
@@ -428,6 +428,8 @@
         break;
     }
 
+    if (aID == eColorID_WindowBackground) aColor = NS_RGB(0xFF,0xFF,0xFF);
+
     return res;
 }