Netscape reads your .mailcap and .mime.types
files at startup time.
If you have Netscape already running you can still reload these files
by selecting General Preferences under menu entry
Options and next select Helper Applications.
In this dialog you check the filename for your .mailcap
file and click OK. The Netscape program will re-read the
.mailcap and .mime.types files once you hit
the OK button.