Depending on the version of Java and your Mozilla browser, the Java plugin may be disabled in the Firefox or Sea Monkey Add-ons Manager or the Java plugin may require Click to Play (CTP) activation. 
If you only see the Java Deployment Toolkit plugin listed in the Add-ons Manager, then Java is not properly detected.
De-selecting this option will prevent Java applets from running in any browser and the Java plugin will no longer appear in the Firefox or Sea Monkey Add-ons Manager or about:plugins list.
To view or change this option, click the Java icon in the Windows Control Panel or Mac OS X System Preferences to open the Java Control Panel, then select the Security tab.    Mac OS: You can download Java from Apple Support Downloads (Java 6 and below). Windows and Linux: You can download Java here or you can select the offline (full) installer for your operating system from this download page.
Mozilla applications are regularly updated for security and stability; however, Mozilla does not provide updates for plug-ins.
Plug-ins can cause crashes and hangs and may contain security vulnerabilities.