If I set my retina MacBook as my primary display and click a download link on my external monitor I see this squashed downloads dialog. If I do the opposite primary/link click combination I see a much larger downloads dialog. There is a similar add-ons bug 1387340, maybe a similar Linux bug 1228570 and possibly related Windows bug 1354102 and bug 1396807. The other bugs don't appear to be getting worked on and have people asking about them recently.