This should result in a new button appearing in a separate toolbar in the Editor. When you click that - it will print all of your files, but show you the print preview window for each, so you will need to click the OK button for each file you want to print. If you want to "print all" silently - open the .js file in e.g. notepad and uncomment the indicated line.
I'd also like to say thanks for the script, it works great! Saves quite a bit of time. Would be even better if you could just hit the print button once without having to worry about the Print dialog box appearing for every document. Do you know if this feature will still be implemented? It seems like this post was from a long time ago and the icon is still greyed out.
One more thing, can I change the java script icon from a puzzle to a printer icon to make it easier for people to know what the icon does?