[MdRipple] does not work on buttons in Firefox

[anckaertr]

Steps to reproduce

simply add a button on a page.

Which browser?

Firefox 57.x, Firefox 58.x

What is expected?

the ripple effect

What is actually happening?

Nothing

[Samuell1]

Doesnt work only if md-button element is button because elements inside button doesnt have events.

[Soletiq]

+1 please fix