Sometimes, for no apparent reason, when scrolling, all the open tabs disappear and I get the desktop with a strip of icons for each open tab that disappear when

Scrolling down an open page, just reading, suddenly I'm looking at my desktop screen with a strip of icons showing open tabs. Move the mouse to the icons in the center of the screen and they either disappear or bring up the tab I don't want. Try to move to the tab I do want and they all disappear! Click on the desktop. Go down to task bar to reopen. Or close the tab that won't go away. It's maddening. Why did this appear? Where is it from? I don't remember downloading it and there is no x to close it or anything when I right click on it.

Of course, I can never make it do it so I can take a screen shot. Totally random. But happening a lot.