Very recently, each time I launch Firefox an arrow appears, pointing downward and quickly disappears to the top of the screen. I'm not in the process of downloading anything, it just happens every time I launch Firefox. At first I thought I was seeing things, but checked it out by just concentrating to catch it appear and disappear. Can't see any reason for this. I've use Firefox for years and it's never happen before. By the way, it does not appear on my IE browser.