Merge: Cleanup lib/dom

Merge: Cleanup lib/dom

This part was required while developing some change in the spec of default parameter (see #1453)
But this series of commit seems good enough and could be independently useful.
It also remove all warnings in the lib/dom directory

Pull-Request: #1616
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>