Same here, I was losing my mind at first. I thought my mouse was acting up. Still no luck. I believe it started happening after the software update, but I haven't found a fix yet. It only triggers in full screen mode. For now, I'm just moving the mouse quickly of the screen and then back to the tabs, which seems to bring everything back, but it's really annoying. Already tried using firefox and chrome, but they both got issues on its own, so i'm stuck with opera...