arrow keys stop working to scroll pages

arrow keys stop working to scroll pages

Sometimes, the arrow keys stop working to scroll pages. Sometimes, in Firefox -> Tools -> Options -> Advanced -> Accessibility -> General, the first checkbox, about using arrow keys to scroll pages, appears checked and some other times, unchecked. When it's unchecked, I check it. When it's checked, I keep it checked. In both times, I click OK. Then, the arrow keys restart working to scroll pages. I'm having to do it all the time. What should I do?