--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -1079,16 +1079,22 @@ nsLookAndFeel::EnsureInit()
     // Require GTK 3.20 for client-side decoration support.
     sCSDAvailable = gtk_check_version(3, 20, 0) == nullptr;
     if (sCSDAvailable) {
         sCSDAvailable =
             mozilla::Preferences::GetBool("widget.allow-client-side-decoration",
                                           false);
     }
 
+    // We need to initialize whole CSD config explicitly because it's queried
+    // as -moz-gtk* media features.
+    sCSDCloseButton = false;
+    sCSDMaximizeButton = false;
+    sCSDMinimizeButton = false;
+
     if (sCSDAvailable) {
         static auto sGtkHeaderBarGetDecorationLayoutPtr =
           (const gchar* (*)(GtkWidget*))
           dlsym(RTLD_DEFAULT, "gtk_header_bar_get_decoration_layout");
 
         GtkWidget* headerBar = GetWidget(MOZ_GTK_HEADER_BAR);
         const gchar* decorationLayout =
             sGtkHeaderBarGetDecorationLayoutPtr(headerBar);