Hi hhal, no it's not supposed to launch notepad, it's supposed to launch your web browser to view the HTML code.

If it launches notepad it must mean that your system is configured for notepad to be the handler for the .htm file extension.

In order to fix that up you'll need to update your system's file association for the .htm file extension, and tell it to use Firefox to open .htm files instead of notepad. You can set the options for that in Windows 8.1 as described here:
http://windows.microsoft.com/en-us/windows-8/choose-programs-windows-uses-default

or also some more details on how to do it here:
http://winsupersite.com/article/windows8/windows-8-tip-change-file-associations-144102

- Michael