diff --git a/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php b/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
index fcdceba..1c72b4f 100644
--- a/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
+++ b/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
@@ -146,6 +146,7 @@ class Selenium2Factory implements DriverFactory
                         ->arrayNode('switches')->prototype('scalar')->end()->end()
                         ->scalarNode('binary')->end()
                         ->arrayNode('extensions')->prototype('scalar')->end()->end()
+                        ->arrayNode('prefs')->prototype('variable')->end()->end()
                     ->end()
                 ->end()
                 ->arrayNode('extra_capabilities')