Month select show insufficient options in Firefox

In Firefox 62.0.3 (tested on both Mac and Linux) the year select does not show as scrollable when clicked open. This behavior can be seen on the example site here (use Firefox obviously) http://amsul.ca/pickadate.js/date/#selectors

Strangely, you can still move backward through the years by successively choosing the earliest year available. So:

1. Open year dropdown, 2018 is currently selected.
1. Choose 2013. Dropdown closes.
1. Reopen dropdown, now the options go back to 2008.
1. Choose 2008.
1. Reopen droddown, now the options go back to 2003.
1. etc.

Here's the markup that's generated.


Works fine in Chrome.