This add-on works good. In fact, it works 'too' good. Indeed there is a button for enable or disable the scrollbar, but it will become a nuisance when Firefox closed and re-opened. It will hide the scrollbars as default at Firefox re-open even though in the previous session I have select "show" when closing the browser. When I want to show the pages' scrollbars as a default I'd have to open Add-On option and disable the extension. In general it need to have a "default show" or "default hide" option.