Java-related issues

This article is no longer maintained, so its content might be out of date.

This article describes and may help to resolve some specific issues related to Java. For general information on installing, enabling, and updating Java, see Use the Java plugin to view interactive content on websites.

Java does not work in Firefox

Starting in Firefox 3.6 you need the new Java plugin that is included in Java 6 Update 10 and above. If you are using an older version of Java, you will need to update your Java plugin. For more information about this change, see Why do I need Java 6 Update 10 and above for Firefox 3.6 and later versions?.

Java applet causes backwards or jumbled typing in text boxes

Sometimes running a Java applet during the browser session can cause the cursor to behave erratically when you type in a text field, so that your text will display backwards or jumbled. Additionally, you may not be able to copy text to the clipboard. If you are having these problems, exit Firefox completely (or restart the computer) and then reopen Firefox.

Java on Windows Vista

Older versions of the Java Runtime Environment may cause Firefox to hang. To resolve the issue, download the latest version of the Java Runtime Environment (JRE) from and manually install it.

Memory use

All versions of Java can consume large amounts of memory, and JRE 5 versions may use substantially more memory than JRE 6. If you are concerned about high memory usage, update Java to the latest available version.

Java applet causes Firefox process to remain in memory

When you close Firefox after running a Java applet, Firefox may remain in memory. When Firefox is restarted, a Close Firefox dialog may appear, including the following message:

Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.

To address this issue, try the following:

  1. Allow the Java applet to fully load before closing Firefox.
  2. Exit the page where the Java applet was loaded before closing Firefox. For example, click the Back button or visit a different web page before exiting Firefox.
  3. Update to the latest version of Java.

Missing plugin alert even though Java is installed

After you have successfully installed Java on your Windows machine, you may see a missing plugin alert or a symbol that looks like a puzzle-piece on pages containing Java applets. The issue is that you may be missing a registry entry that Firefox normally installs.

The solution is to re-install the latest version of Firefox, which also updates the Windows registry. For more information, see How to install Firefox on Windows.

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