This is fixed on any version of Firefox I can test with. Try forcing a refresh with ctrl+f5.
I think Mozilla introduced a bug in 46.0 with the way elements are hit-tested when in a perspective transform. Specifically when preserve-3d is on, the mouse doesn't seem to interact with any elements in the affected blocks in the usual ways. I was unable to confirm whether or not this is a bug, but the behavior as of FF 46 contradicts the behavior in <=45.0, Chrome, and IE 11 so I must assume it is.
I may attempt to isolate the behavior and submit it to Bugzilla, but short term I've changed the HTML so that the clickable elements are outside the parallax effect. This required a CSS update as the selectors had to change.