diff --git a/lib/notifications.js b/lib/notifications.js
index 349afd7..e203237 100644
--- a/lib/notifications.js
+++ b/lib/notifications.js
@@ -23,10 +23,17 @@ exports.notify = function({url, errorStack, messageId}, {lists, notificationPref
 		var tab, tabBrowser;
 		if (browser){
 			window = tabUtils.getOwnerWindow(browser);
+			if (!window){
+				return;
+			}
 			tab = tabUtils.getTabForBrowser(browser);
+			if (!tab){
+				// page ist displayed in preview
+				return;
+			}
 			tabBrowser = tabUtils.getTabBrowser(window);
 		}
-		else if (window){		
+		else if (window){
 			tab = tabUtils.getTabForContentWindow(window);
 			tabBrowser = tabUtils.getTabBrowserForTab(tab);
 			browser = tabUtils.getBrowserForTab(tab);