diff --git a/modules/base.js b/modules/base.js
index dc313af5..456385a2 100644
--- a/modules/base.js
+++ b/modules/base.js
@@ -888,7 +888,7 @@ var TreeStyleTabBase = inherit(TreeStyleTabConstants, {
  
 	setTabValue : function TSTBase_setTabValue(aTab, aKey, aValue) 
 	{
-		if (!aValue)
+		if (aValue === null || aValue === undefined || aValue === '')
 			return this.deleteTabValue(aTab, aKey);
 
 		aTab.setAttribute(aKey, aValue);
diff --git a/modules/window.js b/modules/window.js
index 07f05652..45b68f10 100644
--- a/modules/window.js
+++ b/modules/window.js
@@ -321,7 +321,7 @@ TreeStyleTabWindow.prototype = inherit(TreeStyleTabBase, {
  
 	setWindowValue : function TSTWindow_setWindowValue(aKey, aValue) 
 	{
-		if (!aValue)
+		if (aValue === null || aValue === undefined || aValue === '')
 			return this.deleteWindowValue(this.window, aKey);
 
 		try {