".modal-content" spacing inconsistencies

Trying to find a viable fix for this but struggling so far. I'd appreciate if someone else could pitch in...

The top margin on the first element and bottom margin on the last element are not effective on Firefox. However, they are in Chrome - which causes some spacing inconsistencies. This is more noticeable when there's enough content to fill the containing <div> and trigger a scroll bar. You can see the discrepancy between the two browsers below:

Firefox (44.0.2)

Chrome (49.0.2623.87)