commit a0ccc19
Author: Martin Stransky <stransky@redhat.com>
Date:   Wed Mar 18 07:14:00 2015 -0400

    Bug 1144643 - Render tooltips as transparent on Gtk3. r=karlt
    
    --HG--
    extra : rebase_source : 23085532b27350ca71cbe18db071628388003f33
---
 widget/gtk/nsNativeThemeGTK.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git widget/gtk/nsNativeThemeGTK.cpp widget/gtk/nsNativeThemeGTK.cpp
index e5e1867..26d13a5 100644
--- widget/gtk/nsNativeThemeGTK.cpp
+++ widget/gtk/nsNativeThemeGTK.cpp
@@ -1528,9 +1528,15 @@ nsNativeThemeGTK::GetWidgetTransparency(nsIFrame* aFrame, uint8_t aWidgetType)
   case NS_THEME_MENUPOPUP:
   case NS_THEME_WINDOW:
   case NS_THEME_DIALOG:
-  // Tooltips use gtk_paint_flat_box().
+    return eOpaque;
+  // Tooltips use gtk_paint_flat_box() on Gtk2
+  // but are shaped on Gtk3
   case NS_THEME_TOOLTIP:
+#if (MOZ_WIDGET_GTK == 2)
     return eOpaque;
+#else
+    return eTransparent;
+#endif
   }
 
   return eUnknownTransparency;