diff --git a/content/treestyletab/hacks.js b/content/treestyletab/hacks.js
index c53a6b09..feb8231b 100644
--- a/content/treestyletab/hacks.js
+++ b/content/treestyletab/hacks.js
@@ -247,8 +247,8 @@ TreeStyleTabService.overrideExtensionsOnInitBefore = function TSTService_overrid
 		}
 		eval('gBrowser.mTabContainer.ensureTabIsVisible = '+
 			replaceHorizontalProps(gBrowser.mTabContainer.ensureTabIsVisible.toSource().replace(
-				'tabhbox.boxObject.width < 250',
-				'$& && !gBrowser.treeStyleTab.isVertical'
+				'boxObject.width < 250',
+				'$& || gBrowser.treeStyleTab.isVertical'
 			))
 		);
 		eval('gBrowser.mTabContainer.isTabVisible = '+