TITIE: Highlighting not working on Firefox when CSS has `user-select: all`

Description
go to any page with text that has CSS user-select: all e.g. https://jsfiddle.net/tLm2sx0v/
hover over it (using modifier key if you have one enabled)
nothing happens
works on chrome, only broken on firefox

Browser version
Firefox 85.0.2

Yomichan version
Yomichan 21.1.31.1