If you're making a grognak-compatible mod on Windows, it's handy if your computer treats .ftl files like zipped folders. To make this happen in windows, type the following into a command prompt:
If you're using Vista or later, you'll need to do that from a command prompt with admin privileges. To get one of those, open up your start menu, type cmd in the search box, and press control+shift+enter (some kind of "are you sure?" window should pop up).