Bug 962855 - fix scrollbar appearing in default set on Australis, r=mconley

--HG--
extra : rebase_source : 746fc5d0509752856047e3827c9514a01082ea1f

browser/themes/shared/customizableui/panelUIOverlay.inc.css

@@ -510,7 +510,9 @@ toolbarpaletteitem[place="palette"] > #search-container {
      of 3px. */
   min-width: calc(@menuPanelWidth@ / 3 - 2px);
   max-width: calc(@menuPanelWidth@ / 3 - 2px);
-  height: auto;
+  /* We'd prefer to use height: auto here but it leads to layout bugs in the panel. Cope:
+     1.2em for line height + 2 * .5em padding + margin on the label (2 * 2px) */
+  height: calc(2.2em + 4px);
   max-height: none;
   -moz-box-orient: horizontal;
 }