Background window bleed through

[Robert Moskowitz]

I am seeing shadow content that is a real distraction.

Say I have a terminal window open that does not take up the full screen.

Behind that I have Firefox or Libre Word where much of the window is 
white space.

Behind that I have a Firefox of Libre Calc window with lots of stuff.

I see the content of that 3rd window as shadow stuff in the white space 
of the 2nd window.

Very distracting.

Plus when I use the Alt-Tab, I see shadow text behind the Alt-Tab dialog 
when I am busy looking for the right icon to switch to.

Very distracting.

What do I tweek?