Counteract smooth scrolling on breadcrumbs
Smooth scrolling browsers (Firefox) use the relative area to determine how much scroll to apply. Because breadcrumbs are short vertically, the scroll amount is minimal (3 units) in the Y direction. On browsers which don't smooth scroll the units are usually much higher (100 in Chrome on Win 10). Users seem to expect the scrolling to be quicker due to the horizontal space on breadcrumbs, so we add a bit more power to their scroll when it looks small.
Fixes https://github.com/vector-im/riot-web/issues/9394
