Mac OS X, Windows XP / Windows Vista and Linux.
Version 3.5 or later.
Firedocs ships with Jing for RelaxNG validation and schema-driven insert helpers. For XML editing with schema support make sure you have at least Java 5 Update 12 installed. You can test your Java setup at the Sun Java Test Page. Also make sure you have the Java Browser Plugin installed and enabled. See Firefox > Settings > Content > Java for your current settings.