Bugzilla

Steps to reproduce:
 1. Go to [this bus timetable page](https://www.buseireann.ie/inner.php?id=406&form-view-timetables-from=Clifden+(Library)&form-view-timetables-to=Letterfrack+(Veldons)&form-view-timetables-route=&form-view-timetables-submit=1), or any page which has a vertically-scrollable subframe on a vertically-scrollable page.
 2. Scroll down the outer page until you see the subframe / the bus timetable. (This hides the dynamic toolbars.)
 3. In the bus timetable, scroll down a little bit, and then scroll up a little bit.

Expected results:
The outer page should remain the way it was, only the subframe should be scrolled.

Actual results:
When scrolling up inside the subframe by just the tiniest amount, the toolbars reappear fully, and cause the entire page to shift down. This is very disorienting.

In the attached screen recording, I was reading the second row of the table, and wanted to scroll back up to the first row ("Westport Railway Station"). But the page shifted so that both row 1 and row 2 are now hidden!

Steps to reproduce:
 1. Go to [this bus timetable page](https://web.archive.org/web/20240815050702/https://www.buseireann.ie/inner.php?id=406&form-view-timetables-from=Enniscorthy+(Templeshannon)&form-view-timetables-to=Dublin+Airport+(Atrium+Rd+Zone+10)&form-view-timetables-route=&form-view-timetables-submit=1), or any page which has a vertically-scrollable subframe on a vertically-scrollable page.
 2. Scroll down the outer page until you see the subframe / the bus timetable. (This hides the dynamic toolbars.)
 3. In the bus timetable, scroll down a little bit, and then scroll up a little bit.

Expected results:
The outer page should remain the way it was, only the subframe should be scrolled.

Actual results:
When scrolling up inside the subframe by just the tiniest amount, the toolbars reappear fully, and cause the entire page to shift down. This is very disorienting.

In the attached screen recording, I was reading the second row of the table, and wanted to scroll back up to the first row ("Westport Railway Station"). But the page shifted so that both row 1 and row 2 are now hidden!