In Firefox, the code bound to 'mousemove.vol' throws an error when the mouse leaves the page area while being held down.

The error is TypeError: target.closest is not a function. It's caused by event.target not being the object that the code expects, so it doesn't have the closest method.

This can be observed here: https://www.loc.gov/item/jukebox-5742/. Click and move the volume slider, then, while still holding the mouse button down, move the mouse pointer outside the page (such as up to the address bar.