Issue voting buttons look ugly on Firefox 52.9

Summary

Icons on the buttons are huge.

screen

Steps to reproduce

  1. Open Firefox 52.9.0 ESR on Linux X11;
  2. Go to some issue on gitlab.com
  3. Look at the buttons

Example Project

sultanahamer/OpenContacts#85 (closed)

Possible fixes

Revert some incompatibe design changes. The problem started happening relatively recently.