Yes, but preview is pretty much pointless now as you can edit your text in full screen mode anyway...

Just click the third button on the toolbar and you are in full screen mode. 

 

IMO, a WYSIWYG editor pretty much defeats the point in having a preview option as you're already seeing pretty much what you'll get anyway - Hence the name!

Additionally, I don't see why previewing in full screen is so important since when viewing the page live, there's rarely going to be *nothing* else on the page anyway, so why would you want to preview it that way???

The only real advantage of full screen, in whatever mode, is the ability to see more of youu content at once, which the fullscreen editing feature (as described before) does anyway...

Whatever floats your boat I guess.  ;=)