Index: /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.cpp	(revision 56931)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.cpp	(revision 56932)
@@ -3327,4 +3327,26 @@
                          pPropWidget->window()->winId());
 }
+
+/* static */
+void VBoxGlobal::representAsToolbar(QWidget *pWidget)
+{
+    /* Get display: */
+    Display *pDisplay = pWidget->x11Info().display();
+
+    /* Prepare a name of the property as the key: */
+    Atom net_wm_window_type = XInternAtom(pDisplay, "_NET_WM_WINDOW_TYPE", false);
+    /* Prepare a type of the property as the value: */
+    Atom net_wm_window_type_toolbar = XInternAtom(pDisplay, "_NET_WM_WINDOW_TYPE_TOOLBAR", false);
+
+    /* Populate values array: */
+    long data[1];
+    data[0] = net_wm_window_type_toolbar;
+
+    /* Assign the property for the passed widget: */
+    XChangeProperty(pWidget->x11Info().display(),
+                    pWidget->window()->winId(),
+                    net_wm_window_type, XA_ATOM, 32,
+                    PropModeReplace, (unsigned char*)&data, 1L);
+}
 #endif /* Q_WS_X11 */
 
Index: /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.h
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.h	(revision 56931)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/globals/VBoxGlobal.h	(revision 56932)
@@ -363,4 +363,6 @@
     /** X11: Ensures @a pPropWidget become transient for the @a pWidget. */
     static void setTransientFor(QWidget *pWidget, QWidget *pPropWidget);
+    /** X11: Represents @a pWidget as X11 tool-bar. */
+    static void representAsToolbar(QWidget *pWidget);
 #endif /* Q_WS_X11 */
 
Index: /trunk/src/VBox/Frontends/VirtualBox/src/widgets/UIMiniToolBar.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/widgets/UIMiniToolBar.cpp	(revision 56931)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/widgets/UIMiniToolBar.cpp	(revision 56932)
@@ -321,4 +321,18 @@
     if (QX11Info::isCompositingManagerRunning())
         setAttribute(Qt::WA_TranslucentBackground);
+#endif /* Q_WS_X11 */
+
+#ifdef Q_WS_X11
+    /* Certain WMs requires some X11 magic
+     * to make tool-bar be always-on-top
+     * of corresponding machine-window. */
+    switch (vboxGlobal().typeOfWindowManager())
+    {
+        case X11WMType_Mutter:
+            VBoxGlobal::representAsToolbar(this);
+            break;
+        default:
+            break;
+    }
 #endif /* Q_WS_X11 */