To see an example of the resolution changing, go to fullscreen mode and back. You could also try making the window half as wide and then going to fullscreen mode. This exploits a stamp bug that causes the quality of stamped costumes to vary based on the resolution of the stage. This method has been derived mostly through experimentation, so it might sometimes be off by a few pixels. This has been tested on Windows 10 Chrome & Firefox and iOS 13 Safari. This is surprisingly simpler and more precise than I thought it'd be. However, it's much slower than I'd like. This also might not work in the future, since it depends on a bug. I'm also surprised @qucchia hasn't already done this...
