How to configure Netscape Navigator to use helper applications:
Add description (this can be anything), for example, Maple Worksheet.
Decide on a mime-type, for example, application/x-maple (this complies with current convention), or application/maple.
The suffix that identifies the file (in this case) mws.
Go to handled by subwindow and choose application in the text area write something like xmaple %s (or if that doesn't work try something like /opt/maple/bin/maple -x %s, or use browse to find where the maple application is) the first part is the way you start the application on the local machine the %s is needed it is replaced by the file that you are opening.
Choose ok twice to get out.
After you do all this you will probably have a file mailcap or .mailcap or something similar somewhere which will have a new entry:
application/x-maple;/opt/maple/bin/maple -x %s
and a file mime.types or .mime.types or something similar somewhere which will have a new entry:
desc="Maple Worksheet" \
So if you are bold you can actually go and edit these by hand.