Does not work on Firefox 57

About: Youtube Storyboard
This script does not work for me at the time of writing. There is no preview when mousing over a video thumbnail on YouTube. I am guessing that the script broke with the Firefox 57 and Greasemonkey 4.0.

The script's version is 1.3.1r1605101704 and I am on Windows 10 64-bit, Firefox 57.0.1 64-bit and Greasemonkey 4.0.