Firefox on Windows - Layout bug in sidebar 'Download' buttons

[redrun45]

The green buttons in the sidebar on the 'Page' view (Download, iTunes, RSS, and Torrent) don't always line up as they should on Firefox.

This bug, so far, has only appeared with Firefox on Windows. Also, it only happens when the zoom level is 90%, 70%, or 50% - and not the zoom levels in between. Firefox on Android and on Ubuntu don't seem to have the same issue, nor does any Chromium-based browser we've tested so far.

The expected appearance (at 100% zoom):

A bugged layout (at 90%):