Similar effect as if you sent the following to all windows...
SystemWindowDropShadowRemoval.1.cs
From the preamble:
In (at least) Squeak 4.4, if the preference #menuAppearance3d is set, then SystemWindows too will draw drop shadows. This changeset stops that behavior, and also removes all drop shadows from all existing morphs as a postscript. Menus should continue to honor the #menuAppearance3d preference even after this changeset is loaded, but this has not been heavily tested.