Closing, I don't think this is a C2 bug. Our old native engine sometimes dropped frames in windowed mode, because to v-sync 100% accurately means synchronising every 16ms to <1ms accuracy, and often OS tasks or other software steal just a little bit too much CPU time and it misses the sync. The visual appearance is one frame being displayed twice as long as it ought to (32ms instead of 16ms) every couple of seconds, which if you are watching with hawk eyes is just about noticeable as a "hiccup" or "jank". In real games like Space Blaster though, usually it's virtually impossible to notice, since the motion is slower and the contrast is lower. There's not much to be done other than boost the process priority. Going in to fullscreen (F11) might actually help, since the browser might boost its own priority when fullscreen, as well as closing all other running apps.