What steps will reproduce the problem?
1. Load:

<a href="#">a</a>
<div style="height: 100px; overflow: scroll;">
  scroll down to see some content!<br><br><br>
  <br><br><br>here it is.
</div>

2. Hit tab-key twice.

What is the expected result?
First <a> is focused, then the <div>. (Works in Firefox.)

What happens instead?
Tab-key cannot focus the <div>.

Accessibility implications:
Users are forced to use a mouse pointer to fully read the page's content.

Spec violation:
The HTML spec states that "scrollable regions of elements that are being rendered and are not expressly inert" = focusable areas. And: 
"The CSS 'overflow' property's 'scroll' value typically creates a scrollable region."

https://html.spec.whatwg.org/multipage/interaction.html#focusable-area