How to determine element overflowing in Firefox with box-sizing: border-box?

I want to determine if the element is overflowing, and the standard el.clientWidth < el.scrollWidth works pretty well in Chrome, but for some reason, it has some problems in Firefox.

My guess

My element has box-sizing: border-box + some 0.75rem padding. When the element has an overflow that falls exactly in this 0.75rem, Firefox visualizes the overflow, but the scrollWidth isn’t changing.

Why do I think so? Because clientWidth in Chrome is changing when I change the box-sizing property, and the opposite in Firefox.

Playground

So how could I check the overflow state of one element which will work in all browsers?