Two days ago when I logged onto my computer, I saw that the vertical scrollbar was no longer there. I rebooted my computer, and still there is no scrollbar. I am not sure what to do, but I really miss the scrollbar. Any advice?
It is possible that the screen is too wide or too high and that the scroll bars fall off.
Open the system menu via Alt+Space and see if you can resize that window.
If that works then close Firefox to save that setting.