See video thumbnails, ratings and other details when you mouse over a Youtube link from almost any website
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A day has passed and it surprisingly returned to work OK. Maybe Youtube is making changes on these days and it sometimes breaks the script.
[UPDATE - strangely it returned to work] Stopped working even on the Classic layout
I used this script on the YouTube Classic layout (Polymer Disable) until recently . Now it stopped working. Pale Moon 28.8.4 Greasemonkey for Pale Moon 3.31.4