Chrome (49): <img width="30" alt="screen shot 2016-03-16 at 10 22 36" src="https://cloud.githubusercontent.com/assets/1185269/13815472/11c36cee-eb61-11e5-98b4-0a5b1491ec25.png"> Firefox: <img width="28" alt="screen shot 2016-03-16 at 10 23 43" src="https://cloud.githubusercontent.com/assets/1185269/13815499/33f4030a-eb61-11e5-8514-7a7d7833f6dc.png"> The mixed mark is slightly larger on FF than chrome. It seems that ensuring the px value for width is always an integer fixes this.