Many web pages use Java applets for interactive content such as online games. Before Firefox can run Java applets you must have the Java plugin properly installed and enabled. Java is a programming language that can run on Windows, Mac, Linux, and other computer systems. This article will help you install or update Java and get it working in Firefox.
Java for Windows includes an automatic update feature that periodically checks for updates and notifies you when an update is available for installation. You can view or change your update settings in the Update tab of the Java Control Panel, where you can also manually check for updates. For more information, see the Java Help page, What is Java Auto Update? How do I change notify settings?.
To eliminate potential security vulnerabilities and to save disk space, you should remove any older Java versions that may still be installed. For more information, see the Java Help page How do I uninstall Java on my Windows computer?.
Java is installed with the operating system. To update Java, use the Mac OS X Software Update feature.
Java is not installed by default. To install the latest version of Java, go to the download page at java.com. See the Java Help page How do I install Java for my Mac? for system requirements and installation instructions.
To update Java, go to your Apple System Preferences, click the Java icon to launch the Java Control Panel, then go to the Update tab and click on the Update Now button. See the Java Help page How do I update Java for my Mac? for details.
See Oracle's Manual Installation and Registration of Java Plugin for Linux article for help installing or updating Java on your Linux system.
To test whether Java is installed and enabled in Firefox, visit one of these Java test pages:
If Java is not working, make sure that the Java plugin is enabled in the Add-ons Manager:
Click the menu button and choose Add-ons. The Add-ons Manager tab will open.
If Java is installed but doesn't work, try these solutions:
If the Java plugin does not appear in the Add-ons Manager, even though Java is installed, try each of the following, one at a time, and then reopen Firefox to see if that resolves the problem:
With Firefox completely closed, delete (or rename) the pluginreg.dat file, located in the Firefox profile folder (it will be regenerated once you restart Firefox but any other plugins you may have disabled will be enabled). See Re-initializing the plugins database for detailed instructions.
The Java 7 plugin will only run in 64-bit browsers so confirm that you aren't running Firefox in 32-bit mode.
Make sure the box in front of Open in 32-bit mode is not checked (if it is, clear the checkbox).
Starting in Java 7, the Java Control Panel includes the Security option, "Enable Java content in the browser", which is selected by default. De-selecting this option will prevent Java applets from running in any browser and the Java plugin will no longer appear in the Firefox Add-ons Manager. Make sure that Enable Java content in the browser is selected in the Java Control Panel Security tab. See this Java Help page for details.
On 64-bit Windows, if you only have the 64-bit version of Java installed, the Java plugin will not be available. Current Firefox releases are 32-bit browsers and you will need to install the 32-bit version of Java.
Mozilla browsers use plugin scanning to locate installed plugins so you should make sure that the plugin.scan.plid.all preference has not been disabled:
In the address bar, type about:config and press EnterReturn.
In some cases, after updating from an earlier Java version to Java 7 Update 10 or above, the Java(TM) Platform plugin is no longer detected. This can be caused by a conflict with Java and a standalone installation of JavaFX that prevents the Java plugin from being properly registered. To resolve the problem, uninstall JavaFX. For more information, see this java.com help page.
If Java is installed and enabled (see above) but isn't working properly, try the following:
Make sure that multiple versions of the Java(TM) Platform plugin are not being detected. For example, if Java 7 Update 51 is currently installed, the Java(TM) Platform plugin in the Add-ons Manager tab should be listed as Java(TM) Platform SE 7 U51. If you see other "Java(TM) Platform" versions listed, uninstall the older versions (see How do I uninstall Java on my Windows computer?) or else remove them manually (see Manually uninstalling a plugin).
Even if Java is installed and enabled in Firefox, it may be blocked by other software or Firefox add-ons, for example:
Based on information from Java (mozillaZine KB)