Fixed Android issues when mutation events aren't supported.

src/dispatcher.js

@@ -145,7 +145,12 @@ var dispatcher = {
     }
   },
   contains: /*scope.external.contains || */function(container, contained) {
-    return container.contains(contained);
+    try {
+      return container.contains(contained);
+    } catch(ex) {
+      // most likely: https://bugzilla.mozilla.org/show_bug.cgi?id=208427
+      return false;
+    }
   },
 
   // EVENTS

src/installer.js

@@ -40,7 +40,7 @@ Installer.prototype = {
     // a removal without an insertion when a node is redistributed among
     // shadows. Since it all ends up correct in the document, watching only
     // the document will yield the correct mutations to watch.
-    if (targeting.canTarget(target)) {
+    if (this.observer && targeting.canTarget(target)) {
       this.observer.observe(target, OBSERVER_INIT);
     }
   },