Improved, re:  Regarding: https://bugzilla.mozilla.org/show_bug.cgi?id=1092375

Not worth changing, but for next time…  :)
``` js
[for (a of x) for (b of y) a+'.'+b]
Array [ "1.a", "1.b", "1.c", "2.a", "2.b", "2.c", "3.a", "3.b", "3.c" ]
```