diff --git a/content/treestyletab/hacks.js b/content/treestyletab/hacks.js
index 5ba5be81..4d05cb98 100644
--- a/content/treestyletab/hacks.js
+++ b/content/treestyletab/hacks.js
@@ -693,7 +693,7 @@ TreeStyleTabService.overrideExtensionsOnInitAfter = function TSTService_override
 
 	// Focus Last Selected Tab 0.9.5.x
 	// http://www.gozer.org/mozilla/extensions/
-	this.extensions.checkAvailable('focuslastselectedtab@gozer.org', { ok : function() {
+	this.extensions.isAvailable('focuslastselectedtab@gozer.org', { ok : function() {
 		TreeStyleTabService.registerTabFocusAllowance(function(aTabBrowser) {
 			return !aTabBrowser.selectedTab.hasAttribute('lastselected');
 		});
@@ -1099,7 +1099,7 @@ TreeStyleTabService.overrideExtensionsOnInitAfter = function TSTService_override
 
 	// Remove New Tab Button
 	// https://addons.mozilla.org/firefox/addon/10535
-	this.extensions.checkAvailable('remove-new-tab-button@forerunnerdesigns.com', { ok : function() {
+	this.extensions.isAvailable('remove-new-tab-button@forerunnerdesigns.com', { ok : function() {
 		document.documentElement.setAttribute(TreeStyleTabService.kHIDE_NEWTAB, true);
 	}});
 
diff --git a/content/treestyletab/treestyletabbrowser.js b/content/treestyletab/treestyletabbrowser.js
index 22def261..a658e2e7 100644
--- a/content/treestyletab/treestyletabbrowser.js
+++ b/content/treestyletab/treestyletabbrowser.js
@@ -1796,7 +1796,7 @@ TreeStyleTabBrowser.prototype = {
 			this.getPref('extensions.informationaltab.thumbnail.position') < 100
 			) {
 			let self = this;
-			this.extensions.checkAvailable('informationaltab@piro.sakura.ne.jp', {
+			this.extensions.isAvailable('informationaltab@piro.sakura.ne.jp', {
 				ok : function() {
 					aStyle = 'retro';
 					self.setTabbrowserAttribute(self.kTWISTY_STYLE, aStyle);
diff --git a/modules/extensions.js b/modules/extensions.js
index 6e87fc5c..cd10c7df 100644
--- a/modules/extensions.js
+++ b/modules/extensions.js
@@ -92,7 +92,7 @@ if (typeof window == 'undefined') {
 			return addon;
 		},
 
-		_formatCallbacks : function()
+		_formatCallbacks : function(aOKCallback, aNGCallback)
 		{
 			var callbacks = {
 					ok : aOKCallback,