diff --git a/content/treestyletab/group.js b/content/treestyletab/group.js
index 5dbee009..32933aa8 100644
--- a/content/treestyletab/group.js
+++ b/content/treestyletab/group.js
@@ -174,7 +174,7 @@ function onItemClick(aEvent)
 
 	if (isMiddleClick)
 		gBrowser.removeTab(tab);
-	else if (button != 2)
+	else if (event.button != 2)
 		gBrowser.selectedTab = tab;
 }
 
diff --git a/modules/fullTooltip.js b/modules/fullTooltip.js
index 507c7105..fbea5d78 100644
--- a/modules/fullTooltip.js
+++ b/modules/fullTooltip.js
@@ -178,7 +178,7 @@ FullTooltipManager.prototype = {
 
 				if (isMiddleClick)
 					this.owner.browser.removeTab(tab);
-				else if (button != 2)
+				else if (event.button != 2)
 					this.owner.browser.selectedTab = tab;
 			}
 		}