diff --git a/src/selenium/firefox/capabilities.cr b/src/selenium/firefox/capabilities.cr
index e84f6b1..0ecc729 100644
--- a/src/selenium/firefox/capabilities.cr
+++ b/src/selenium/firefox/capabilities.cr
@@ -11,5 +11,6 @@ class Selenium::Firefox::Capabilities < Selenium::Capabilities
     end
 
     property args = [] of String
+    property binary String?
   end
 end