I like the "internal" preview, it is fast and refresh automatically but since I have a laptop with a dual screen (fairly common nowdays) I would like to have the preview detachable (outside the editing window) so I can put the preview into another screen.
If I have a web page that does not fit into a screen I have to scroll manually each time every time I change the content. It would be great if the caret/cursor on the preview was in the same "location" as the editing cursor.