Mozilla Firefox before 2.0.0.17 and 3.x before 3.0.2, and SeaMonkey before 1.1.12, allow user-assisted remote attackers to move a window during a mouse click, and possibly force a file download or unspecified other drag-and-drop action, via a crafted onmousedown action that calls window.moveBy, a variant of CVE-2003-0823.