When launching via the new launcher the JVM argument -Dorg.lwjgl.opengl.Window.undecorated=true isn't working. It was working on the old launcher just fine. The version I lanched it with specifically with was 1.7.10 but this shouldn't be affected by version launched. The aim of this jvm argument is to remove the top bar with the minimize, maximise and exit buttons and other parts to allow for you to create a borderless windowed when using windows + up to fullscreen it.