Make scrollbars on posts visible please?

The new side-by-side post format has some benefits, but I keep getting hung up on the invisible scrollbars. Could you please make them visible again? I keep missing comments past the first page, or the rest of a post past the first page.

I remember someone saying "that's just how your browser or OS renders them", but it ain't so. I'm on Firefox on Linux, not a Mac, and I get those weird thin Mac-ish scrollbars on Imzy but not on other sites.