I believe that Firefox includes its own copy of Java. You can disable it by going to Tools -> Add Ons and disabling Java there.
Of course, even with that enabled, you still would need a Java web applet plug-in, which my copy of Firefox does not have. Try testing here:
These are where the OS installs Java components (might not be all of them, but finding those is left as an exercise). BTW, there's no good reason to remove any of them.
Java Web Start.app