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I'm trying to play this on Windows 10 - I'm new to DOSBox.

It works okay, but as soon as I ALT-TAB out of it, the MoM window shrinks to a tiny size and worse, my mouse stops working in that window.

Any tips? Is it a DOSBox setting?
budfudder: Any tips? Is it a DOSBox setting?
Both are DOSBox things. To return to full screen, press Alt-Tab. To get the mouse working again, click inside the game's window.