Comment 23 for bug 327863

I'm tempted to take the patch in comment #7 except that it won't work when the vertical scrollbar is on the left-hand side.

Setting the availableHeight is a bad idea since that can trigger page breaking.

How about just changing nsScrollbarFrame::Reflow so that if it is a reflow root (i.e. its aReflowState has no parentReflowState), then we just save its current size on entry and set aDesiredSize to that size on exit, thus ensuring that the presshell assertions are not fired and presumably fixing this bug?