diff --git a/content/treestyletab/treestyletab.js b/content/treestyletab/treestyletab.js
index c836b506..989c54a9 100644
--- a/content/treestyletab/treestyletab.js
+++ b/content/treestyletab/treestyletab.js
@@ -1310,9 +1310,7 @@ catch(e) {
 		event.initEvent('TreeStyleTabSubtreeClosing', true, true);
 		event.parent = aParentTab;
 		event.tabs = aClosedTabs;
-		this.ensureEventCancelable(event);
-		this.getTabBrowserFromChild(aParentTab).dispatchEvent(event);
-		return !event.getPreventDefault();
+		return this.getTabBrowserFromChild(aParentTab).dispatchEvent(event);
 	},
  
 	fireTabSubtreeClosedEvent : function TSTService_fireTabSubtreeClosedEvent(aTabBrowser, aParentTab, aClosedTabs) 
diff --git a/modules/utils.js b/modules/utils.js
index 503e30a3..be23b0ea 100644
--- a/modules/utils.js
+++ b/modules/utils.js
@@ -412,22 +412,6 @@ var TreeStyleTabUtils = {
  
 // event 
 	
-	ensureEventCancelable : function(aEvent) 
-	{
-		if (aEvent.getPreventDefault) return;
-		// getPreventDefault is available on any event on Gecko 1.9.2 or later.
-		// on Gecko 1.9.1 or before, UIEvents only have the method...
-		aEvent.__original__preventDefault = aEvent.preventDefault;
-		aEvent.__canceled = false;
-		aEvent.preventDefault = function() {
-			this.__original__preventDefault();
-			this.__canceled = true;
-		};
-		aEvent.getPreventDefault = function() {
-			return this.__canceled;
-		};
-	},
- 
 	isNewTabAction : function TSTUtils_isNewTabAction(aEvent) 
 	{
 		return aEvent.button == 1 || (aEvent.button == 0 && this.isAccelKeyPressed(aEvent));