Version: 49.0.2623.112
OS: Ubuntu 14.04

What steps will reproduce the problem?
(1) Open https://jsfiddle.net/LLcf4od9/1/

What is the expected output?
The spinner animation is vertically stable

What do you see instead?
Vertical jitter of the spinner, so that it even displays a previous frame edge sometimes. My guess is that it's related to some rounding errors when recomputing the background position for each frame.

This works just fine with FF 45 - no vertical jitter.