See this: <br /> http://lists.apple.com/archives/java-dev/2011/Jun/msg00115.html Looks like Apple broke Java in 10.5.8 for Firefox 3.6+ versions by removing Plugin2. "With this release, we have greatly enhanced the functionality of Plugin2 on Mac OS X 10.6, but this came at the cost of having to remove Plugin2 from Mac OS X 10.5, due to the lack of necessary OS graphics primitives and the capabilities of J2SE 5.0. We are looking forward to making Plugin2 the default applet plug-in in the near future, so please let us know if there are show stopping issues that prevent your applets from running inside it."