Hello. In v6.49 @ECLASS is v6.46, in v6.51 -- v6.46, in v6.53 -- v6.52. Please fix.
commit 6f44cfc997b8c83e5ca211fdb34387b433d78a66 Author: Lars Wendler <polynomial-c@gentoo.org> Date: Fri Oct 13 10:54:29 2017 mozconfig-v.6*.eclass: Fixed @ECLASS description (bug #618906).