We recently came across a situation in our markup where we wanted whitespace in the markup for readability, but we didn't want that whitespace represented between the elements.
We found a fix that suggested using font-size: 0 in CSS to eliminate the whitespace. That worked fine in Chrome, but we found that in Firefox, the containing element no longer scrolled with the mouse wheel or arrow keys! Apparently Firefox's scroll speed is proportional to font-size.