Windows artifact on desktop won't disappear

[peppergomez]

EDIT---nevermind. Rebooted and it went away.

Love this artifact that has appeared on my desktop and won't go away, and overlays any app or file I have open.

I was moving the mouse rapidly and meant to open a new tab in Firefox, and also dragged the mouse a bit, which resulted in this lovely artifact. I have refreshed my desktop but this #%&*$# won't go away.

Any suggestions?