Updating java applet
Many web pages use Java applets for interactive content such as online games. Starting in Firefox 3.6, Java will not work unless you are using the Next-Generation Java Plug-In (included in Java 6 Update 10 and above).
To run these Java applets, you need the "Java Runtime Environment" ("JRE") installed and enabled.  Important: Mozilla adds outdated or insecure plugins to its Add-ons Blocklist as a security measure.
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. 
See below for more information on installing or updating Java on Windows.See 64 bit builds for more information about 64-bit versions of Mozilla applications.   Note: The Java Embedding Plugin has been bundled with Mac distributions of older Mozilla browsers, including Firefox 3.x and Sea Monkey 2.0. If you don't need 64-bit Java, there is no reason to have it installed.If both 32-bit and 64-bit versions of Java are installed, the Windows Control Panel will display only the 64-bit Java Control Panel.This utility allows browsers other than Apple's Safari to use the most recent versions of Java on Mac OS X. The Java Embedding Plugin is no longer needed in newer Mozilla browsers such as Firefox 4 and is no longer included.Information on security and stability issues affecting Java is available at Oracle's Critical Patch Updates and Security Alerts page.Java is a programming language originally developed by Sun Microsystems (now Oracle).After enabling Java, test Java again: The Java Deployment Toolkit plugin, which is installed along with Java, does NOT need to be enabled for Java applets to work.If you only see the Java Deployment Toolkit plugin listed in the Add-ons Manager, then Java is not properly detected.