I am "guessing" that this started after I upgraded to 10.9.5? I am on a 2011 17" Macbook Pro. All of a sudden I notice that if I move my cursor to the far left of the screen a black transparent overlay (about 3") wide pops out? It seems to list all the open Safari windows and FTP App windows, etc., but not other open apps (like the dock I have at the bottom)? What is this and can I turn it off? I am not seeing anything like this on my desktop MacPro running the same OS version?