First let's test if Java works. Goto http://java.com and click on this link "Do I have Java?" and Verify Java version. If you see something like this, then you have Java plugin enabled.
How to disable it?
Goto Tools -> Manage Add-ons -> Toolbars and Extensions, select to show all add-ons and you will see addons from Oracle America, Inc. You may see more or less of these plugins. Disable Java(tm) Plug-In SSV Helper and if you are unsure if you must disable other plugins, choose "More information" and if you see somewhere Java or JRE, disable it.
Now go back into java.com and see if Java works and now you should see that no working Java was detected, so you successfully disabled it.