Sometime between 2.32.0 and r275506, mouse wheel scrolling broke pretty badly. It still works, but scrolls only a tiny portion of the page, far less than it is supposed to scroll.
I'm not quite done bisecting yet, but I think it's likely to be r273733 "Eliminate ScrollAnimatorGeneric::m_smoothAnimation"
OK, I've narrowed this down to r273733-273735, and I don't think it's 273734 or 273735. Probably some silly mistake hidden somewhere in r273733 "Eliminate ScrollAnimatorGeneric::m_smoothAnimation".
Let's do a revert until scrolling devs have more time to look into it. *** This bug has been marked as a duplicate of bug 224686 ***