I have seen this issue in the archives, but not much mention of it anywhere else.
I just thought I would let everyone know that I tried to get this working by adding "fullscreen" to the "plugins" and "theme_advanced_buttons1" options in the file "cms/javascript/tinymce.template.js".
I reloaded the site and bam! Working fullscreen editing (at least for me).
I am curious though, is there a reason this was left out? Are there issues with adding it that meant it needed to be left out? Will it bring down the internet?
Ta,
Mo