Bug 1501560 - Port bug 1501235 to TB: Move menubar autohide code from xul.css to messenger.css. r=jorgk

mail/base/content/messenger.css

@@ -243,6 +243,18 @@ splitmenu {
   -moz-binding: url("chrome://messenger/content/mailWidgets.xml#appmenu-vertical") !important;
 }
 
+%ifndef XP_MACOSX
+toolbar[type="menubar"][autohide="true"] {
+  overflow: hidden;
+}
+
+toolbar[type="menubar"][autohide="true"][inactive="true"]:not([customizing="true"]) {
+  min-height: 0 !important;
+  height: 0 !important;
+  -moz-appearance: none !important;
+}
+%endif
+
 /* Preferences */
 
 preftab,