Facebook vertical scroll bar problems on Safari, iCab, SeaMonkey

On a Facebook page under Safari, multiple clicks (5-10) on the vertical scroll bar get into a mode in which the scroll bar jumps around randomly and the main page jumps with it. This problem occurs on our 2016 MacBook Pro under Monterey 12.6.2 and our 2022 M2 MacBook Air under Ventura 13.1. It also occurs on the iCab browser on both machines, and under the SeaMonkey browser on the Pro/Monterey (no SeaMonkey for M2). It does not occur on any of our other 8 browsers including Chrome, Firefox, etc. The problem settles out after a while (it takes more jumping on Safari than iCab or SeaMonkey).

I have no idea where to send this problem. Any suggestions?