commit 57f29e7b6c5f1b0f16cc6991e57634bf64a16c9e
Author: Simon Steinbeiss <simon.steinbeiss@elfenbeinturm.at>
Date:   Sat Apr 4 14:45:01 2015 +0200

    Try to fix Firefox's tooltips in Gtk3

diff --git a/gtk-3.0/gtk-widgets.css b/gtk-3.0/gtk-widgets.css
index dca2b28..3af0c11 100644
--- a/gtk-3.0/gtk-widgets.css
+++ b/gtk-3.0/gtk-widgets.css
@@ -3551,7 +3551,8 @@ GtkColorButton.button {
 /***********
  * tooltip *
  ***********/
-.tooltip {
+.tooltip,
+.tooltip.background {
     border-width: 1px;
     border-style: solid;
     border-color: alpha(@theme_tooltip_bg_color, 0.9);