diff --git a/content/treestyletab/treestyletab.js b/content/treestyletab/treestyletab.js
index 01b888eb..995af1f0 100644
--- a/content/treestyletab/treestyletab.js
+++ b/content/treestyletab/treestyletab.js
@@ -448,19 +448,26 @@ var TreeStyleTabService = {
 			this.setTreePref('enableSubtreeIndent.horizontal', !this.getTreePref(pref));
 	},
  
-	changeTabbarPosition : function(aNewPosition) /* PUBLIC API */ 
+	changeTabbarPosition : function(aNewPosition) /* PUBLIC API (obsolete, for backward compatibility) */ 
 	{
-		if (!aNewPosition || !/^(top|bottom|left|right)$/i.test(aNewPosition))
-			aNewPosition = 'top';
-
-		aNewPosition = aNewPosition.toLowerCase();
-		this.setTreePref('tabbar.position', aNewPosition);
+		this.currentTabbarPosition = aNewPosition;
 	},
  
 	get currentTabbarPosition() /* PUBLIC API */ 
 	{
 		return this.getTreePref('tabbar.position') || 'top';
 	},
+	set currentTabbarPosition(aValue)
+	{
+		var position = String(aValue);
+		if (!position || !/^(top|bottom|left|right)$/i.test(position))
+			position = 'top';
+
+		position = position.toLowerCase();
+		this.setTreePref('tabbar.position', position);
+
+		return aValue;
+	},
   
 /* backward compatibility */ 
 	getTempTreeStyleTab : function(aTabBrowser)
diff --git a/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js b/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
index 68093f58..7a5bcd70 100644
--- a/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
+++ b/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
@@ -34,7 +34,7 @@ TreeStyleTabBrowserTabpanelDNDObserver.prototype = {
 				let orient = (position == 'left' || position == 'right') ? 'vertical' : 'horizontal' ;
 				sv.setTreePref('tabbar.fixed.'+orient, false);
 			}
-			sv.changeTabbarPosition(position);
+			sv.currentTabbarPosition = position;
 		}
 
 		aEvent.stopPropagation();