I didn't use ampersand gt. The browser (IE, at least) doesn't get confused when it hits a ">" without first hitting a "<", so you can go ahead & use ">" alone.
To produce "</sarcasm>", I enclosed it in <xmp></xmp> tags. That tells the browser to not interpret anything within the tags.
Also note, when you quote some text that has either < or <xmp> blocks or other sneaky html tricks, often the tricks get lost or translated into weird variations by the browser, and the effect is lost or totally mangled. (Or maybe it's FR's posting code which feels like it does some pretranslation of its own.)