I'm seeing breakthrough of the background when Firefox is open on my second monitor. This seems to occur when the window on the secondary monitor is minimised, then maximised and mouse over the image on the secondary monitor (second is right hand side) - see image. Initially I thought this was a graphics issue but this does not occur when I repeat the steps with other applications. I have also tried it with Chrome and Chrome does not display the same behaviour. I do not see this behaviour on the primary monitor. I have reduced the refresh rate from 144Hz to 60Hz and reset Firefox which has not cured the issue. It appears to me that the only application that exhibits this behaviour on this machine is Firefox. I also started to see this occur on my previous machine which was based on Mint 17 and a different Nvidia GPU and monitors and had been stable for many years. If there is any further information I can provide, please let me know as I'm loathed to change from Firefox as I've been a fan for many years.