E4X was implemented in SpiderMonkey (Gecko's JavaScript engine) since version 1.6.0[6] until version 20, and is in Rhino (Mozilla's other JavaScript engine written in Java instead of C) since version 1.6R1.[7] As Mozilla Firefox is based on Gecko, older versions could be used to run scripts using E4X. But this feature is deprecated since release 16 and removed in release 18. Adobe's ActionScript 3 scripting language fully supports E4X.