MutationObserver failed in some instances

Fixes #354

lib/iframeProtection.js

@@ -123,8 +123,11 @@
 			var observer = new MutationObserver(allCallback);
 			var observing = false;
 			function observe(){
-				if (!observing){
-					observer.observe(window.document.documentElement, {subtree: true, childList: true});
+				if (
+					!observing &&
+					window.document
+				){
+					observer.observe(window.document, {subtree: true, childList: true});
 					observing = true;
 				}
 			}

releaseNotes.txt

@@ -12,6 +12,7 @@ Version 0.5.10:
 		- not connected iFrame threw error with persistent rng
 		- detection over document.write and document.writeln was possible
 		- google docs were broken in Waterfox
+		- MutationObserver failed in some instances
 	
 	known issues:
 		- if a data URL is blocked the page action button does not appear