When you hold your mouse and go up, you slide up infinitely.
This might be expected behavior - at least, Opera does the same.
Seems like this is a bug since certain scrolling methods like text selection and anchor links work on overflow: hidden documents (do anchor links scroll overflow:hidden elements within a document?) but "normal" ones like the mouse wheel and up/down arrows and page up and page down do not. The intention of overflow:hidden seems to just be to hide scrollbars, not disable all scrolling functionality entirely.
This bug is caused by 22769.
The newer bug has a bit more discussion in it, marking this one as duplicate. *** This bug has been marked as a duplicate of 22769 ***