Comment 8 for bug 744580

After doing some digging today, I realised that this only ever worked in 3.6 because the statusbar made it possible for the pointer to travel beyond the end of the scrolled area.

This is caused because nsTypedSelection::DoAutoScroll calls PresShell::ScrollFrameRectIntoView with a 1x1 nsRect (in app units). This means that the pointer needs to travel beyond the edge of the scrolled area before that nsRect is out of view (which is what triggers scrolling).

To fix this, you can make the nsRect passed to ScrollFrameRectIntoView a bit larger. I've attached a patch which does this, which ensures that the nsRect starts to go out of view before the pointer reaches the edge of the scrolled area