diff --git a/firefox/treestyletab.css b/firefox/treestyletab.css
index c1f6d66..98df13a 100644
--- a/firefox/treestyletab.css
+++ b/firefox/treestyletab.css
@@ -76,3 +76,7 @@ tab-item tab-favicon * {
   vertical-align: top;
 }
 
+.highlighter::before {
+  margin-top: -1px;
+  margin-bottom: -1px;
+}