There is a difference between using browser-specific or experimental elements in your documents and writing HTML that produces garbage on every browser but the one you have in mind. If you use browser-specific elements, do not try to avoid problems by telling your reader to "Download NetXploder 4 NOW!", but fix your document so it still works if the browser-specific material is ignored.
If the browser-specific elements you use are essential to the document or cannot degrade gracefully on other browsers, then provide an alternative way to get at the information. For example, if you have a complex table in a document, you can make a screenshot of that table available separately.
