This happens whenever I pull down a page in the forum to refresh (and it doesn’t).
It happens in all the other web pages as well if I try to pull them down.
I think it just started recently with the Firefox update to 130. What it is all about?
From Firefox 130 release notes:
Overscroll animations are now enabled as the default behavior for scrollable areas on Linux.
Ah, I see! Thanks for the pointer and sorry for not having done my homework before posting!