--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -1154,16 +1154,40 @@ nsCSSRuleProcessor::InitSystemMetrics()
   }
 
   rv = LookAndFeel::GetInt(LookAndFeel::eIntID_SwipeAnimationEnabled,
                            &metricResult);
   if (NS_SUCCEEDED(rv) && metricResult) {
     sSystemMetrics->AppendElement(nsGkAtoms::swipe_animation_enabled);
   }
 
+  rv = LookAndFeel::GetInt(LookAndFeel::eIntID_GTKCSDAvailable,
+                           &metricResult);
+  if (NS_SUCCEEDED(rv) && metricResult) {
+    sSystemMetrics->AppendElement(nsGkAtoms::gtk_csd_available);
+  }
+
+  rv = LookAndFeel::GetInt(LookAndFeel::eIntID_GTKCSDMinimizeButton,
+                           &metricResult);
+  if (NS_SUCCEEDED(rv) && metricResult) {
+    sSystemMetrics->AppendElement(nsGkAtoms::gtk_csd_minimize_button);
+  }
+
+  rv = LookAndFeel::GetInt(LookAndFeel::eIntID_GTKCSDMaximizeButton,
+                           &metricResult);
+  if (NS_SUCCEEDED(rv) && metricResult) {
+    sSystemMetrics->AppendElement(nsGkAtoms::gtk_csd_maximize_button);
+  }
+
+  rv = LookAndFeel::GetInt(LookAndFeel::eIntID_GTKCSDCloseButton,
+                           &metricResult);
+  if (NS_SUCCEEDED(rv) && metricResult) {
+    sSystemMetrics->AppendElement(nsGkAtoms::gtk_csd_close_button);
+  }
+
 #ifdef XP_WIN
   if (NS_SUCCEEDED(
         LookAndFeel::GetInt(LookAndFeel::eIntID_WindowsThemeIdentifier,
                             &metricResult))) {
     nsCSSRuleProcessor::SetWindowsThemeIdentifier(static_cast<uint8_t>(metricResult));
     switch(metricResult) {
       case LookAndFeel::eWindowsTheme_Aero:
         sSystemMetrics->AppendElement(nsGkAtoms::windows_theme_aero);