e.g., as I read a webpage, when I push the Page Down keyboard key, sometimes nothing happens; sometimes the page scrolls down a few lines but then doesn't continue to scroll down when I push the key additional times; sometimes the page immediately jumps to the bottom of the page; etc. Similar issues occur, in the up direction, when I push the Page Up key. The Home and End keys are completely "dead", as the page doesn't move when I push them. It's important to note that all of these keys work as usual when I open the Chrome or Internet Explorer browsers, and in all other applications in which the keys should be functional, so this problem is specific to Firefox.