First thing I get when clicking "DoIt" in Chrome or Firefox is "Parse error on line 1 column 47 : Unexpected character null".
Edit: turns out, I should've looked more closely. You're supposed to select particular text before pressing the button. If you do this it works. Still, they might want to consider a more friendly error message ;)
Almost as terrible is the fact that the listed keyboard shortcut alternative to clicking DoIt (CTRL d) actually deletes, rather than executes, the selected text.