When a page that fits into one screen (and so the scroll bar is not present) is zoomed for larger text size (by pressing Ctrl++), if it becomes lager that the screen the scroll bar must appear. But in fact the scroll bar doesn't appear, and a gray bar shows up it its place, therefore it's not possible to use the scroll bar until the page is reloaded.
I tried Phoenix 0.4 and the nightly on November 4th.
Duplicate of Mozilla bug. Changing Product and Component. *** This bug has been marked as a duplicate of 173072 ***