I also get these issues as well. What I notice is that full screen in YouTube at 60 fps is choppy and there is a lot of noise present. Not sure how to fix this...you could try doing Flash Version > go to the "\Maxthon
\Core\Webkit\Npplugins" in the Maxthon installation directory, then rename the file "NPSWF32.dll". After that, Maxthon will use the installed version of Flash Player.