The maximize button doesn't appear for JSViz visuals, nor for any visual that has no title bar. It's possible to maximize visuals by maximizing another one and then cycling through (as long as at least one visual on the page has the button). It would be helpful if there were some way to maximize all visuals regardless of whether they have a suitable title bar.
Pete, many thanks for contributing. For visuals that have no title bar you can right-click in the visual and select Maximize. I do not think this works for JS Viz though, but will check.