--- a/widget/gtk/WidgetStyleCache.cpp
+++ b/widget/gtk/WidgetStyleCache.cpp
@@ -159,16 +159,39 @@ GetWidget(WidgetNodeType aWidgetType)
   if (!widget) {
     widget = CreateWidget(aWidgetType);
     sWidgetStorage[aWidgetType] = widget;
   }
   return widget;
 }
 
 GtkStyleContext*
+CreateStyleForWidget(GtkWidget* aWidget, GtkStyleContext* aParentStyle)
+{
+  GtkWidgetPath* path =
+    gtk_widget_path_copy(gtk_style_context_get_path(aParentStyle));
+
+  // Work around https://bugzilla.gnome.org/show_bug.cgi?id=767312
+  // which exists in GTK+ 3.20.
+  gtk_widget_get_style_context(aWidget);
+
+  gtk_widget_path_append_for_widget(path, aWidget);
+  // Release any floating reference on aWidget.
+  g_object_ref_sink(aWidget);
+  g_object_unref(aWidget);
+
+  GtkStyleContext *context = gtk_style_context_new();
+  gtk_style_context_set_path(context, path);
+  gtk_style_context_set_parent(context, aParentStyle);
+  gtk_widget_path_unref(path);
+
+  return context;
+}
+
+GtkStyleContext*
 CreateCSSNode(const char* aName, GtkStyleContext* aParentStyle, GType aType)
 {
   static auto sGtkWidgetPathIterSetObjectName =
     reinterpret_cast<void (*)(GtkWidgetPath *, gint, const char *)>
     (dlsym(RTLD_DEFAULT, "gtk_widget_path_iter_set_object_name"));
 
   GtkWidgetPath* path = aParentStyle ?
     gtk_widget_path_copy(gtk_style_context_get_path(aParentStyle)) :

--- a/widget/gtk/WidgetStyleCache.h
+++ b/widget/gtk/WidgetStyleCache.h
@@ -16,16 +16,23 @@ typedef unsigned StyleFlags;
 enum : StyleFlags {
   NO_STYLE_FLAGS,
   WHATEVER_MIGHT_BE_NEEDED = 1U << 0,
 };
 
 GtkWidget*
 GetWidget(WidgetNodeType aNodeType);
 
+/*
+ * Return a new style context based on aWidget, as a child of aParentStyle.
+ * If aWidget still has a floating reference, then it is sunk and released.
+ */
+GtkStyleContext*
+CreateStyleForWidget(GtkWidget* aWidget, GtkStyleContext* aParentStyle);
+
 // CreateCSSNode is implemented for gtk >= 3.20 only.
 GtkStyleContext*
 CreateCSSNode(const char*      aName,
               GtkStyleContext* aParentStyle,
               GType            aType = G_TYPE_NONE);
 
 // Callers must call ReleaseStyleContext() on the returned context.
 GtkStyleContext*

--- a/widget/gtk/mozgtk/mozgtk.c
+++ b/widget/gtk/mozgtk/mozgtk.c
@@ -513,16 +513,17 @@ STUB(gdk_device_manager_get_client_point
 STUB(gdk_disable_multidevice)
 STUB(gdk_device_manager_list_devices)
 STUB(gdk_display_get_device_manager)
 STUB(gdk_error_trap_pop_ignored)
 STUB(gdk_event_get_source_device)
 STUB(gdk_window_get_type)
 STUB(gdk_x11_window_get_xid)
 STUB(gdk_x11_display_get_type)
+STUB(gtk_box_new)
 STUB(gtk_cairo_should_draw_window)
 STUB(gtk_cairo_transform_to_window)
 STUB(gtk_combo_box_text_append)
 STUB(gtk_drag_set_icon_surface)
 STUB(gtk_get_major_version)
 STUB(gtk_get_micro_version)
 STUB(gtk_get_minor_version)
 STUB(gtk_menu_button_new)
@@ -568,16 +569,17 @@ STUB(gtk_style_context_set_direction)
 STUB(gtk_style_context_set_path)
 STUB(gtk_style_context_set_parent)
 STUB(gtk_style_context_set_state)
 STUB(gtk_style_properties_lookup_property)
 STUB(gtk_tree_view_column_get_button)
 STUB(gtk_widget_get_preferred_size)
 STUB(gtk_widget_get_state_flags)
 STUB(gtk_widget_get_style_context)
+STUB(gtk_widget_path_append_for_widget)
 STUB(gtk_widget_path_append_type)
 STUB(gtk_widget_path_copy)
 STUB(gtk_widget_path_free)
 STUB(gtk_widget_path_new)
 STUB(gtk_widget_path_unref)
 STUB(gtk_widget_set_visual)
 STUB(gtk_app_chooser_dialog_new_for_content_type)
 STUB(gtk_app_chooser_get_type)

--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -1137,17 +1137,26 @@ nsLookAndFeel::Init()
     sMozWindowText = GDK_RGBA_TO_NS_RGBA(color);
     gtk_style_context_restore(style);
     g_object_unref(style);
 
     // tooltip foreground and background
     style = ClaimStyleContext(MOZ_GTK_TOOLTIP);
     gtk_style_context_get_background_color(style, GTK_STATE_FLAG_NORMAL, &color);
     sInfoBackground = GDK_RGBA_TO_NS_RGBA(color);
-    gtk_style_context_get_color(style, GTK_STATE_FLAG_NORMAL, &color);
+    {
+        GtkStyleContext* boxStyle =
+            CreateStyleForWidget(gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 0),
+                                 style);
+        GtkStyleContext* labelStyle =
+            CreateStyleForWidget(gtk_label_new(nullptr), boxStyle);
+        gtk_style_context_get_color(labelStyle, GTK_STATE_FLAG_NORMAL, &color);
+        g_object_unref(labelStyle);
+        g_object_unref(boxStyle);
+    }
     sInfoText = GDK_RGBA_TO_NS_RGBA(color);
     ReleaseStyleContext(style);
 
     // menu foreground & menu background
     GtkWidget *accel_label = gtk_accel_label_new("M");
     GtkWidget *menuitem = gtk_menu_item_new();
     GtkWidget *menu = gtk_menu_new();