Question screen tearing on a windowed game

[luh4ren]

I play a Flash game called Transformice, and for some reason, it stutters on my 144 Hz monitor. I used to play without any problems in the past using the same monitor and even worse specs (not that it should matter for a 2D Flash game). Surprisingly, when I set my monitor's refresh rate to 120 Hz, the game becomes much smoother, but not permanently—there is still occasional screen tearing that prevents me from playing properly. I've also tried turning Adaptive Sync on and off on my monitor, but it doesn't change anything. However, when I put the game in fullscreen with Adaptive Sync on, there is a lot of flickering that makes it impossible to play.