For exactly same purpose I am grooming self-contained HTML Sandbox "datauri app" [0] living in my bookmarks that too retains its state in location (#hash) so is copypastable to other browsers. I like to load preview to isolated iframe and have single editor. (Not as golfed as xem's ([1]) but it's mine and I like its few extra features.)

[0] https://gist.github.com/myfonj/c8ce74bf549e19600026ce9022388... [1] http://xem.github.io/miniCodeEditor/