Since a couple weeks back templating is also implemented¹, just lacking tagged templates and documentation²³.
1: https://bugzilla.mozilla.org/show_bug.cgi?id=688857#c22
2: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...
3: https://developer.mozilla.org/en-US/docs/Web/JavaScript/ECMA...
Firefox Nightly currently supports just enough of template strings to give you multiline strings.