If you are on a 64-bit Windows machine and are getting a notification that your Java plugin version is out of date in Firefox even after installing the latest version, you need to install the 32-bit version of Java.
Firefox runs as a 32-bit application on Windows, so it uses the 32-bit version of Java. I should have read the fine print on the Java website. It tells you to install both 64 and 32-bit versions if you are on a 64-bit system, but are running a 32-bit browser. I did, and now my Java version is up to date in Firefox.
If you are on a 64-bit Windows machine and run Firefox, you may want to make sure you are upgraded to the latest version of 32-bit Java. You can find out by going to the Addons Manager in Firefox, clicking the “Plugins†tab on the left, then click the “Check to see if your plugins are up to date†link at the top of the page. If Java is out of date, it will give you a red warning.