Fix top border in Firefox (#280)

Author: marie-bnl

usr/share/webapp-manager/firefox/profile/chrome/userChrome.css

@@ -4,4 +4,8 @@
 
 #nav-bar * {
     visibility: visible !important;
-}
+}
+
+#navigator-toolbox {
+    border-bottom: none !important;
+}