When I try to close Netscape Nitro I get an error message that I have to close Netscape or Mozilla as well.

For resolution of this common error message, see the question "Netscape Nitro doesn't work with the Netscape or Mozilla browsers". To avoid seeing this message, we recommend that subscribers who use Netscape/Mozilla browsers leave Nitro on once their computer is turned on and not stop/disable it when browsing.