--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -1660,17 +1660,27 @@ NS_IMETHODIMP nsWindow::SetSizeMode(PRIn
         // If sTrimOnMinimize is set, we let windows handle minimization normally
         // using SW_MINIMIZE.
         mode = sTrimOnMinimize ? SW_MINIMIZE : SW_SHOWMINIMIZED;
         break;
 
       default :
         mode = SW_RESTORE;
     }
-    ::ShowWindow(mWnd, mode);
+
+    WINDOWPLACEMENT pl;
+    pl.length = sizeof(pl);
+    ::GetWindowPlacement(mWnd, &pl);
+    // Don't call ::ShowWindow if we're trying to "restore" a window that is
+    // already in a normal state.  Prevents a bug where snapping to one side
+    // of the screen and then minimizing would cause Windows to forget our
+    // window's correct restored position/size.
+    if( !(pl.showCmd == SW_SHOWNORMAL && mode == SW_RESTORE) ) {
+      ::ShowWindow(mWnd, mode);
+    }
     // we dispatch an activate event here to ensure that the right child window
     // is focused
     if (mode == SW_RESTORE || mode == SW_MAXIMIZE || mode == SW_SHOW)
       DispatchFocusToTopLevelWindow(NS_ACTIVATE);
   }
   return rv;
 }