After looking into this for firefox CI failure.

With the following snippet:

<textarea id="pass8" name="textarea" aria-label="test">
  hazaar
  hazaar
  hazaar
</textarea>

Within scrollable-region-focusable we call getScroll() which calls this function isScrollable().

Here we check the scrollableX and scrollableY values have the scroll or overflow prop;

With Chrome we get:

{overflowProp: 'auto'}

Interestingly, with Firefox we get (unless we explicitly add style: "overflow: auto") :

{ overflowProp: "visible" }

I was not sure if adding visible to the overflowProp include check had possible negative side effects - possibly requires more discussion 👀

\cc @WilcoFiers / @straker