diff --git a/skin/classic/treestyletab/treestyletab-3.1.css b/skin/classic/treestyletab/treestyletab-3.1.css
index 3020c299..8a4dfae1 100644
--- a/skin/classic/treestyletab/treestyletab-3.1.css
+++ b/skin/classic/treestyletab/treestyletab-3.1.css
@@ -4,11 +4,11 @@
 
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="default"] .tabbrowser-tab,
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="mixed"] .tabbrowser-tab {
-	-moz-box-shadow: -5px 0 5px rgba(0, 0, 0, 0.15) !important;
+	-moz-box-shadow: -5px 5px 5px rgba(0, 0, 0, 0.15) !important;
 }
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="default"][treestyletab-appearance-inverted="true"] .tabbrowser-tab,
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="mixed"][treestyletab-appearance-inverted="true"] .tabbrowser-tab {
-	-moz-box-shadow: 5px 0 5px rgba(0, 0, 0, 0.15) !important;
+	-moz-box-shadow: 5px 5px 5px rgba(0, 0, 0, 0.15) !important;
 }
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="default"]:not([treestyletab-hide-newtab-button]) .tabs-container:not([overflow="true"]) .scrollbox-innerbox,
 tabbrowser[treestyletab-mode="vertical"][treestyletab-style="mixed"]:not([treestyletab-hide-newtab-button]) .tabs-container:not([overflow="true"]) .scrollbox-innerbox {