Pop-up graphic artifacts

Hello, I am using linux mint. Sometimes when I use the browser is youtube video flies and I play for example a game then I see sometimes some squares on the firefox screen. It also happens that when I use firefox on two monitors I will see such squares. Recently I used with virtualbox firefox it is a virtual machine was running and separately the browser and the computer crashed. I do not know how to collect possible logs that something like this happened, these squares.