In Firefox on Linux (44.0.2), Wave 3 don't seem to be working as intended because for the second tower group you've got:

    div.board__tower-group
        div.tower-group__tower
        div.tower-group__tower
        div.board__tower-group--body

and, even though it's `position:absolute`, Firefox is taking that third child into account when applying `justify-content:space-between`, placing the first tower on the left and the second in the center instead of on the right.

Edit: Here's the Firefox bug https://bugzilla.mozilla.org/show_bug.cgi?id=874718