A menu somewhere to select the current media type would be lovely - not least for checking print stylesheets. Perhaps a drop-down at the top of responsive mode?

A nice ui for cookie management stuff (edit, delete) would be good too. Even better would be a way to manage different sets of cookies on the same site - eg per-tab cookies, or an option to save/clear/restore - to make it easier to test as different users at the same time.