JSS is antiquated. Even the inventor eschews support for JSS entirely in favor of the standard CSS2. We are strong proponents of reasonable standards, and now that the CSS2 model is fully supported in HTML 4 and XHTML, we can't recommend that you use anything but CSS-standard stylesheets.
Netscape versions 4 and earlier implemented JSS by extending several existing HTML tags and defining a few objects that store your document's styles. Netscape no longer supports JSS, nor does any other browser.