Firefox and Java downloads

I've got a question about the Java Runtime Environment program. I've
never paid much attention to it in the past, but I know it is an
important plug-in for Firefox. I always thought there was one version
of Java for Windows that would work with all browsers.

Yet if I visit the Java download home page, version 5 update 7 for
Internet Explorer is listed. If I visit the Firefox plug-in page, it
lists Java version 5 update 1. Is it really necessary to install both
versions for both browsers to use Java?

observer20@gmail.com