Not sure what's missing from your setup, but it does work fine with Firefox and Chrome (and IE of course). I'll be doing an updated release within the next week, which will include an updated demo project, so this should get you on your way when it comes.
To use Castle Validator on the server, you need to register the provider, e.g. in your Global.asax.cs file as follows:
protected void Application_Start()
If you don't want to wait for the update next week, then please send me a small VS project that shows client-side validation not working in Firefox or Chrome and I'll see what the problem is.