Underline does not animate away when unfocused on FF on Linux

[e111077]

Description

The underline does not animate away when quickly tabbed through. Only seems to be reproducible on FF v47.0 on linux (works fine on same version of FF on OS X)

Expected outcome

Underline should animate when not focused.

Actual outcome

Underline stops animating when not focused.

Live Demo

http://jsbin.com/qosigiredo/1/edit?html,output

Steps to reproduce

1. Open demo in FF 47.0 on linux
2. Tab quickly through

   Browsers Affected

• [ ] Chrome
• [x] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10