Issue MoonchildProductions/UXP#1578 - Add global menubar support for GTK

toolkit/content/widgets/popup.xml

@@ -25,8 +25,14 @@
         </getter>
       </property>
 
-      <property name="state" readonly="true"
-                onget="return this.popupBoxObject.popupState"/>
+      <property name="state" readonly="true">
+        <getter><![CDATA[
+          if (this.hasAttribute('_moz-nativemenupopupstate'))
+            return this.getAttribute('_moz-nativemenupopupstate');
+          else
+            return this.popupBoxObject.popupState;
+        ]]></getter>
+      </property>
 
       <property name="triggerNode" readonly="true"
                 onget="return this.popupBoxObject.triggerNode"/>

toolkit/content/xul.css

@@ -307,6 +307,15 @@ toolbar[type="menubar"][autohide="true"][inactive="true"]:not([customizing="true
 }
 %endif
 
+%ifdef MOZ_WIDGET_GTK
+window[shellshowingmenubar="true"] menubar,
+window[shellshowingmenubar="true"]
+toolbar[type="menubar"]:not([customizing="true"]) {
+  /* If a system-wide global menubar is in use, hide the XUL menubar. */
+  display: none !important;
+}
+%endif
+
 toolbarseparator {
   -moz-binding: url("chrome://global/content/bindings/toolbar.xml#toolbardecoration");
 }