Capture NS_ERROR_FAILURE errors from Firefox

Author: benvinegar

src/utils.js

@@ -28,6 +28,7 @@ function isEmptyObject(what) {
 function isError(what) {
     return isObject(what) &&
         objectPrototype.toString.call(what) === '[object Error]' ||
+        objectPrototype.toString.call(what) === '[object Exception]' || // Firefox NS_ERROR_FAILURE Exceptions
         what instanceof Error;
 }