I don’t think there’s any browser/JavaScript engine that makes mouse events accessible outside the browser document area.
You can give Slip.js and touch events a try by adding listeners to OpenFL’s canvas element, as it looks like it registers touch movements outside the browser window to a limited extent (but only after a touch/tap has been made)
Thanks, I managed to get it working by adding a mouse move event listener to js.Browser.document instead of an openfl MouseEvent listener on the stage.