What you did in your website's CSS:

* { scrollbar-width: thin; }

Why that's a problem for us, your website's visitors: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/scrollbar-width#accessibility

What we have to do to regain use of our own scrollbars in a mouse-first UI because you overlooked us:

Firefox:

Go to URL: about:config

Search preference name: layout.css.scrollbar-width-thin.disabled

Change from "false" to "true"