Firefox displays modal twice at certain widths

[mjewell]

In Firefox 64.0 at certain widths the modal will render strangely when the isOpen prop is toggled to true. The weird second modal disappears when you click anywhere in the browser. Can be reproduced (regularly, but not completely consistently) by going to the storybook page for modals, setting the central display area to a width of 500px, and toggling the isOpen prop through the knobs panel.

[mjewell]

Once it is reproduced, you can toggle this behaviour on/off by toggling this style:

.modal.show .modal-dialog {
    transform: translate(0);
}